all the textures were hand painted with various brushes. available on my site. did get the colors i would make a new layer, use the airbrush to glaze a color over it, then change the blending mode of the layer itself till something looked cool. remember to adjust the opacity of the layer too. then erase what you don't need then drop the layer.
on the top of the screen click, window > brush. then the brush window will be open. on cs5 its the option called transfer. then under opacity, turn control off. it should be like painting with a mouse, but with the control of a pencil.
this could parallax if used on more of a side scroller type of scenario, the games angle is more isometric and this asset will be manually inserted throughout the environment by the designer so it wouldn't be so modular.