I'm very new to 3D graphics so excuse my lack of knowledge. So from what I understand, there does exist a technique that modifies each polygon's/sprite's colour at an individual pixel level. So in theory, it should be possible to tell a computer to colour each character/object as according to a concept art right? However,…
UDK material examples: http://udn.epicgames.com/Three/MaterialsCompendium.html Custom lighting in UDK (this is what you need if you want to make your "own shader"): http://udn.epicgames.com/Three/CustomLighting.html