War-steed Colour Packs are on sale this week for 50% off. These are expensive, 595 TP regular price, and rarely on sale except for special sales like this one. Colour Packs must be purchased separately for each character!
There are 6 Steed Colour Packs, each of which contains 4 colours that can be used to set your war-steed's hide and tail colour. There are 6 Equipment Dye Packs, each of which contains 4 colours that can be applied to war-steed gear. They are not like dye items in the game. Instead, they simply let you select colours through the Appearance tab of the Mounted Combat panel (M command by default).
There are also several hide patterns you can buy.
If you're going to invest in war-steed colours, now is a good time to do it.