1. Eyes
2. Various parts of your armour.
That's all it affects. I chose purple, because purple goes with everything except orange and green (who wears orange or green armour?) and it is also generally awesome.
As the previous comment says, Vatel sells items (at 50k crowns, ie too much) that let you change your height, personal colour, and eye shape.
After creating your knight the only way to change your personal color is through Vatel by buying a different color for 50kCr.