Tips for painting consistently?

Hello! I've just started making terraino as of a few days ago, but I'm having trouble making the paint stick consistently, 1-1-1 ratio frequently leaves big light patches all over the foam. Is there a particular technique to applying the paint I need to use? Should I use a different ratio? I haven't washed/highlighted them yet but I'm not sure it'll help too much as some parts of the walls/floor are almost totally white. Thanks!