I have also made 2 of these things out of foam board, one for my 127mm and one for the VC200L.
They both work like a dream. I didn't bother painting mine and they are white. I can't see what difference it will make as it is only for focussing and doesn't matter if it gives a bit of dispersion etc.
Total price $16 for the sheet of foam board with a large amount left over for the kids to use on "craft"
