That can be a couple of things.
If the colour is completly even over the whole screen, it can be the VGA Cable. Just swap it with another one and you're good to go.
If it's patchy, then i hope you have warrenty. Epson EMP-74 Projectors, and i think a few others, get a common fault like this. The lens right next to the prisom inside the projector has become burnt. This isn't fixable really. I've not found anyone that can supply the specific part to repair it, and you need to take the projector apart into a million pieces to get to it.
When it happened here, i just got them replaced on Warrenty. When the Warrenty expired, i took one apart and discovered the problem. We just have to replace them now when it happens.