In the 13th century, for infantry you would generally have town militias, feudal troops, feudal levies, and mercenaries.
Just in terms of shields:
Town Militias would either carry the mark of their town, the quarter they lived in, or their guild.
Feudal troops might carry a simplified version of their lords heraldry.
Feudal levies might just carry the primary colour of their lord, or a monotone shield colour, or even just leather or wood.
Mercenaries could have either monotone colours or simple geometric patterns, or if serving long term, the patterns of whomever hired them.
For instance on the Bayeux Tapestry there's a scene in which two milites are fighting on foot with spears in front and behind them are a mass of men also wearing armour and fighting with spears. The men in front have long swords very prominently displayed, and decorated shields. The mass of men behind don't have swords displayed and their shields are monotone in blue, red, or yellow/leather with little multicolour dots on them around the boss. The men in front seem pretty obviously knights, those in back either mercenaries or feudal troops.

In terms of clothing...
It's possible that urban militias might have worn their town or guild colours on their clothing but I don't think others would have. They probably would have had clothing in different colours.
So if I'm painting up some feudal infantry I'd look at the assorted heraldry on my Knights and do the infantry shields in a simple version of those patterns, maybe one or two per. Might throw in some monotone shields and a couple just leather.