I'm not really sure if this can be altered, but I've found that some faction colors are hardcoded, I think, at least they show up slightly altered in the faction-rating scroll.

To quote descr_sm_factions;
;artificially made darker to show up on sm banner
;actual colour is:
;primary_colour red 237, green 234, blue 179
I'm not really sure how the above is meant, I do know that the greek_cities show up white/yellow-ish in the faction-rating scroll (where other factions with similair faction-colours show grey ....)

Not to spoil the fun, but so you may want to test this properly with your colours or possibly pick an other faction to turn purple ..;)


G