As for the color of polystyrene insulation...there is gray? Never seen that one before. I have used both pink and blue and they both work great.As for your wall making question...i am writing an article on how i make maps. The article should cover your question :)http://geekedondungeonsanddragons.com/Cartography-f20/Making-your-own-3d-maps-t631.htm