This isn't new idea and I suppose it was already spoken here in forums, but coudn't find it in "search".
By customization I mean mostly colour of light and middling armours, and some places of heavy armours. My idea is not to add 5 same armours with different colour, but to add dye. You could buy dye for 1k, 5k, maybe for 10-20k (or more to make it elite some way), buy different colours and tint armours like Brigandine, but also e. g. this blue gambeson beneath scale armor or tunic under mail shirt, also materials in heavy armours e. g. in gothic plate or churburg. To dye it in other colour you will have to buy another one.
Good thing would be also steel tone in mails, plates, scales, et cetera. It is a bit annoying, some mails have dark tone, some light, and some even completly other.
It would be good for guys without clan and custom banners, but also will add more diversity to battlefield.