Someone handles the track builder and knows how to paint the blackground

Well, they told me that the race track builder only has the option to paint with 3 textures, that if I wanted more I had to paint the blackground from photoshop, the problem is that I don't know how, because I can paint but with colors, not with textures, but yes I clone a texture, I get super big, thanks

 

Can you show us an example?