They dont sell that at petco. Construction paper is pretty much something little kids use for arts and crafts. I think most houses have some. I know mine does. Go to walmart tonight/tomorrow or whenever and ask for construction paper. It comes in many colors and its cheap. I recomend you stick to these few colors:
-Black(personally I think is the best)
-Brown
-Grey
I mean you could buy a wallpaper but I think they cost more. I may be wrong.