I have started building my round house. The Walthers' kit has a concrete floor that is very shinny. The foundation is part of the red colored plastic that is used for the brick walls and will need to be painted. I was thinking about painting it "aged concrete", but that color is very yellow. I tried adding white to lighten up the yellow color and it is still to yellow. Concrete should be more grey. The regular concrete color makes it look to new. What would you recommend. BTW I am using PollyScale paints. Thanks for any help.