OK, so looking through the files in the Data folder to see what other files needed editing for my mod, I discovered a file which actually set the colour of the sky. I fiddled around with this for a while, and found out some stuff.

OK, now this is a useless but still funny discovery. Take a look in descr_pallete.txt and you will see this.

Code:
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
; Colourmap description file
;
; Setup a number of palettes with an array of colours in each
; The seasonal colourmaps need to have identical entries
; 
; colour values in 0.0 - 1.0 range - Functions exist to translate to 0-255 if necessary
;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

begin_colourmap		winter

;		R	G	B	ID

	colour	0.000	0.000	0.000   sun_midnight		; sun colours (1 for each of the 8 timezones)
	colour	1.000	0.310	0.000   sun_sunrise		
	colour	0.941	0.921	0.490	sun_mid_morn
	colour	1.000	1.000	1.000   sun_morning
	colour	1.000	1.000	1.000   sun_midday
	colour	1.000	1.000	1.000   sun_sunset
	colour	0.941	0.921	0.490	sun_mid_eve
	colour	1.000	0.310	0.000   sun_night	

	colour	0.400	0.400	0.300	midday_sun_light	; light colours
	colour  0.100	0.100	0.100	horizon_sun_light	
	colour	0.000	0.000	0.000   sun_ambient			

	colour	0.350   0.350   0.350	full_moon_light
	colour	0.100	0.100	0.100	new_moon_light
	colour  0.080	0.080	0.080	horizon_moon_light	
	colour  0.010   0.010   0.010   moon_ambient

	colour	0.150	0.150	0.220	ambient_level_night
	colour	0.010	0.010	0.010	ambient_level_day

	colour	0.000	0.000	0.000   fog_midnight		; Fog colours (1 for each of the 8 timezones)
	colour	0.300	0.300	0.300   fog_sunrise
	colour	0.600	0.600	0.600   fog_mid_morn
	colour	0.700	0.700	0.700	fog_morning
	colour	0.800	0.800	0.800	fog_midday
	colour	0.700	0.700	0.700	fog_sunset
	colour	0.600	0.600	0.600   fog_mid_eve
	colour	0.300	0.300	0.300   fog_night

; Skydome colours - For each time of day (8 in total), there are 3 colours required - horizon, midpoint and zenith

	colour	0.000	0.000	0.000	sd_midnight_horiz
	colour	0.000	0.000	0.000	sd_midnight_mid
	colour	0.000	0.000	0.000	sd_midnight_zen

	colour	0.412	0.255	0.600	sd_sunrise_horiz
	colour	0.000	0.118	0.263	sd_sunrise_mid
	colour	0.412	0.255	0.600	sd_sunrise_zen

	colour	0.898	0.361	1.000	sd_mid_morn_horiz
	colour	0.000	0.247	0.549	sd_mid_morn_mid
	colour	0.012	0.000	0.431	sd_mid_morn_zen

	colour	0.847	0.729	0.953	sd_morning_horiz
	colour	0.000	0.443	0.851	sd_morning_mid
	colour	0.020	0.000	0.768	sd_morning_zen

	colour	0.683	0.828	1.000	sd_midday_horiz
	colour	0.000	0.659	1.000	sd_midday_mid
	colour	0.028	0.000	1.000	sd_midday_zen

	colour	0.847	0.729	0.953	sd_sunset_horiz
	colour	0.000	0.443	0.851	sd_sunset_mid
	colour	0.020	0.000	0.768	sd_sunset_zen

	colour	0.898	0.361	1.000	sd_mid_eve_horiz
	colour	0.000	0.247	0.549	sd_mid_eve_mid
	colour	0.012	0.000	0.431	sd_mid_eve_zen

	colour	0.412	0.255	0.600	sd_night_horiz
	colour	0.000	0.118	0.263	sd_night_mid
	colour	0.412	0.255	0.600	sd_night_zen

end_colourmap

begin_colourmap		spring

;			R		G		B		ID

	colour	0.000	0.000	0.000   sun_midnight		; sun colours (1 for each of the 8 timezones)
	colour	1.000	0.310	0.000   sun_sunrise		
	colour	0.941	0.921	0.490	sun_mid_morn
	colour	1.000	1.000	1.000   sun_morning
	colour	1.000	1.000	1.000   sun_midday
	colour	1.000	1.000	1.000   sun_sunset
	colour	0.941	0.921	0.490	sun_mid_eve
	colour	1.000	0.310	0.000   sun_night	

	colour	0.400	0.400	0.300	midday_sun_light	; light colours
	colour  0.100	0.100	0.100	horizon_sun_light	
	colour	0.000	0.000	0.000   sun_ambient			

	colour	0.350   0.350   0.350	full_moon_light
	colour	0.100	0.100	0.100	new_moon_light
	colour  0.080	0.080	0.080	horizon_moon_light	
	colour  0.010   0.010   0.010   moon_ambient

	colour	0.150	0.150	0.220	ambient_level_night
	colour	0.010	0.010	0.010	ambient_level_day

	colour	0.000	0.000	0.000   fog_midnight		; Fog colours (1 for each of the 8 timezones)
	colour	0.300	0.300	0.300   fog_sunrise
	colour	0.600	0.600	0.600   fog_mid_morn
	colour	0.700	0.700	0.700	fog_morning
	colour	0.800	0.800	0.800	fog_midday
	colour	0.700	0.700	0.700	fog_sunset
	colour	0.600	0.600	0.600   fog_mid_eve
	colour	0.300	0.300	0.300   fog_night

; Skydome colours - For each time of day (8 in total), there are 3 colours required - horizon, midpoint and zenith

	colour	0.000	0.000	0.000	sd_midnight_horiz
	colour	0.000	0.000	0.000	sd_midnight_mid
	colour	0.000	0.000	0.000	sd_midnight_zen

	colour	0.412	0.255	0.600	sd_sunrise_horiz
	colour	0.000	0.118	0.263	sd_sunrise_mid
	colour	0.412	0.255	0.600	sd_sunrise_zen

	colour	0.898	0.361	1.000	sd_mid_morn_horiz
	colour	0.000	0.247	0.549	sd_mid_morn_mid
	colour	0.012	0.000	0.431	sd_mid_morn_zen

	colour	0.847	0.729	0.953	sd_morning_horiz
	colour	0.000	0.443	0.851	sd_morning_mid
	colour	0.020	0.000	0.768	sd_morning_zen

	colour	0.683	0.828	1.000	sd_midday_horiz
	colour	0.000	0.659	1.000	sd_midday_mid
	colour	0.028	0.000	1.000	sd_midday_zen

	colour	0.847	0.729	0.953	sd_sunset_horiz
	colour	0.000	0.443	0.851	sd_sunset_mid
	colour	0.020	0.000	0.768	sd_sunset_zen

	colour	0.898	0.361	1.000	sd_mid_eve_horiz
	colour	0.000	0.247	0.549	sd_mid_eve_mid
	colour	0.012	0.000	0.431	sd_mid_eve_zen

	colour	0.412	0.255	0.600	sd_night_horiz
	colour	0.000	0.118	0.263	sd_night_mid
	colour	0.412	0.255	0.600	sd_night_zen

end_colourmap

begin_colourmap		summer

;			R		G		B		ID

	colour	0.000	0.000	0.000   sun_midnight		; sun colours (1 for each of the 8 timezones)
	colour	1.000	0.310	0.000   sun_sunrise		
	colour	0.941	0.921	0.490	sun_mid_morn
	colour	1.000	1.000	1.000   sun_morning
	colour	1.000	1.000	1.000   sun_midday
	colour	1.000	1.000	1.000   sun_sunset
	colour	0.941	0.921	0.490	sun_mid_eve
	colour	1.000	0.310	0.000   sun_night	

	colour	0.400	0.400	0.300	midday_sun_light	; light colours
	colour  0.100	0.100	0.100	horizon_sun_light	
	colour	0.000	0.000	0.000   sun_ambient			

	colour	0.350   0.350   0.350	full_moon_light
	colour	0.100	0.100	0.100	new_moon_light
	colour  0.080	0.080	0.080	horizon_moon_light	
	colour  0.010   0.010   0.010   moon_ambient

	colour	0.150	0.150	0.220	ambient_level_night
	colour	0.010	0.010	0.010	ambient_level_day

	colour	0.000	0.000	0.000   fog_midnight		; Fog colours (1 for each of the 8 timezones)
	colour	0.300	0.300	0.300   fog_sunrise
	colour	0.600	0.600	0.600   fog_mid_morn
	colour	0.700	0.700	0.700	fog_morning
	colour	0.800	0.800	0.800	fog_midday
	colour	0.700	0.700	0.700	fog_sunset
	colour	0.600	0.600	0.600   fog_mid_eve
	colour	0.300	0.300	0.300   fog_night

; Skydome colours - For each time of day (8 in total), there are 3 colours required - horizon, midpoint and zenith

	colour	0.000	0.000	0.000	sd_midnight_horiz
	colour	0.000	0.000	0.000	sd_midnight_mid
	colour	0.000	0.000	0.000	sd_midnight_zen

	colour	0.412	0.255	0.600	sd_sunrise_horiz
	colour	0.000	0.118	0.263	sd_sunrise_mid
	colour	0.412	0.255	0.600	sd_sunrise_zen

	colour	0.898	0.361	1.000	sd_mid_morn_horiz
	colour	0.000	0.247	0.549	sd_mid_morn_mid
	colour	0.012	0.000	0.431	sd_mid_morn_zen

	colour	0.847	0.729	0.953	sd_morning_horiz
	colour	0.000	0.443	0.851	sd_morning_mid
	colour	0.020	0.000	0.768	sd_morning_zen

	colour	0.683	0.828	1.000	sd_midday_horiz
	colour	0.000	0.659	1.000	sd_midday_mid
	colour	0.028	0.000	1.000	sd_midday_zen

	colour	0.847	0.729	0.953	sd_sunset_horiz
	colour	0.000	0.443	0.851	sd_sunset_mid
	colour	0.020	0.000	0.768	sd_sunset_zen

	colour	0.898	0.361	1.000	sd_mid_eve_horiz
	colour	0.000	0.247	0.549	sd_mid_eve_mid
	colour	0.012	0.000	0.431	sd_mid_eve_zen

	colour	0.412	0.255	0.600	sd_night_horiz
	colour	0.000	0.118	0.263	sd_night_mid
	colour	0.412	0.255	0.600	sd_night_zen

end_colourmap

begin_colourmap		autumn

;			R		G		B		ID

	colour	0.000	0.000	0.000   sun_midnight		; sun colours (1 for each of the 8 timezones)
	colour	1.000	0.310	0.000   sun_sunrise		
	colour	0.941	0.921	0.490	sun_mid_morn
	colour	1.000	1.000	1.000   sun_morning
	colour	1.000	1.000	1.000   sun_midday
	colour	1.000	1.000	1.000   sun_sunset
	colour	0.941	0.921	0.490	sun_mid_eve
	colour	1.000	0.310	0.000   sun_night	

	colour	0.400	0.400	0.300	midday_sun_light	; light colours
	colour  0.100	0.100	0.100	horizon_sun_light	
	colour	0.000	0.000	0.000   sun_ambient			

	colour	0.350   0.350   0.350	full_moon_light
	colour	0.100	0.100	0.100	new_moon_light
	colour  0.080	0.080	0.080	horizon_moon_light	
	colour  0.010   0.010   0.010   moon_ambient

	colour	0.150	0.150	0.220	ambient_level_night
	colour	0.010	0.010	0.010	ambient_level_day

	colour	0.000	0.000	0.000   fog_midnight		; Fog colours (1 for each of the 8 timezones)
	colour	0.300	0.300	0.300   fog_sunrise
	colour	0.600	0.600	0.600   fog_mid_morn
	colour	0.700	0.700	0.700	fog_morning
	colour	0.800	0.800	0.800	fog_midday
	colour	0.700	0.700	0.700	fog_sunset
	colour	0.600	0.600	0.600   fog_mid_eve
	colour	0.300	0.300	0.300   fog_night

; Skydome colours - For each time of day (8 in total), there are 3 colours required - horizon, midpoint and zenith

	colour	0.000	0.000	0.000	sd_midnight_horiz
	colour	0.000	0.000	0.000	sd_midnight_mid
	colour	0.000	0.000	0.000	sd_midnight_zen

	colour	0.412	0.255	0.600	sd_sunrise_horiz
	colour	0.000	0.118	0.263	sd_sunrise_mid
	colour	0.412	0.255	0.600	sd_sunrise_zen

	colour	0.898	0.361	1.000	sd_mid_morn_horiz
	colour	0.000	0.247	0.549	sd_mid_morn_mid
	colour	0.012	0.000	0.431	sd_mid_morn_zen

	colour	0.847	0.729	0.953	sd_morning_horiz
	colour	0.000	0.443	0.851	sd_morning_mid
	colour	0.020	0.000	0.768	sd_morning_zen

	colour	0.683	0.828	1.000	sd_midday_horiz
	colour	0.000	0.659	1.000	sd_midday_mid
	colour	0.028	0.000	1.000	sd_midday_zen

	colour	0.847	0.729	0.953	sd_sunset_horiz
	colour	0.000	0.443	0.851	sd_sunset_mid
	colour	0.020	0.000	0.768	sd_sunset_zen

	colour	0.898	0.361	1.000	sd_mid_eve_horiz
	colour	0.000	0.247	0.549	sd_mid_eve_mid
	colour	0.012	0.000	0.431	sd_mid_eve_zen

	colour	0.412	0.255	0.600	sd_night_horiz
	colour	0.000	0.118	0.263	sd_night_mid
	colour	0.412	0.255	0.600	sd_night_zen

end_colourmap
It seems that there are colours set for every season, for every time of day and for every piece of weather. There is one group in each season for regular colours, one for fog and one for the skydome (divided into horizon, midpoint and zenith).

So, after fiddling around a little longer I realized how the colour system works. After the "colour" tag at the beginning of each line there is a set of three numbers, first red, second green, third blue. Now, this does not work like the 0-255 scale which you will usually find colours for. No, this goes from a scale of 0.000 (black when all three colour values are the same I think) to 1.000 (white). To get the colour you want, you must therefore divide each of the values on the 255 RGB scale by 255, ensuring that each number has 3 decimal places. (remember to round)

So, being the kinda guy I am, I decided to test this out by changing the colour value of some of these to completely green. Let's see what I got:



OK, so maybe I only actually managed to change the sun, but still. I think the file is limited to changing the sun, unless we can find another way of doing this.