In sieges - flashing banners and flashing green banners??

Ok, I have experienced two bizarre scenarios during sieges; one where my own unit banners started flashing green during a siege assault and one where my enemy's unit banners started flashing (no colour)during a siege. What I'd like to know is what these mean?

1) The first scenario happened when my units were near walls that my siege weapons were also pounding. Other than my nearby units' banners flashing green, there didn't appear to be any other effect of it...

2) The second scenario was when my mortars smashed down one of my own walls, which was surrounded by enemy units and their ladders. The enemy which had climbed onto the walls died as the walls crumbled and the ladders they'd used fell to the ground. Meanwhile the banners of the rest of the enemy units who were going to climb the ladders just started flashing?! The worst part was that they then did nothing for the rest of the battle....

Any thoughts/help?

Green flashing banners mean that your/the enemies troops are affected by the disease from dead cows launched by trebuchets.