As you can see, "texturing" my hand-drawn papercraft Advance Wars models is just as low-tech as making the actual parts. ;o)
Usually I colour in the black parts first with a permanent marker, drawing the fold lines with a white pencil. After that, I colour the rest of the parts with magic markers in the appropriate colour.
That way, if I need to make five of the same tank (like the Megatanks for example), I can re-use the black template as basis to make the five different colours. But of course, there is only one Blue Moon Tank, so in this case I can colour the original templates directly. ;o)