If you're in the military, you would be issued armor or could commission personal armor that met certain requirements, particularly if you're nobility. The style of armor is dictated by the kingdom. If you were nobility and wanted armor that reflected your family, you would go to a smith that already makes weapons and armor for the kingdom and give him your specifications for custom options. Usually this would be limited colored sashes with embroidered crests, gauntlets with embossed insignia, shields with colored patterns, or even weapons styled to match your race (an elf fighting in a majority human military could have an elven style blade made for them).