Master the brush in Photoshop

Then watch the Screenshots carefully.

I will create a new (top) layer and overlay it with gradient.











The Blending mode here - Multiply.



Here is our current result.



Now I'm still thinking that my picture here is a little bit Planar and 2d. Let's make a new layer between the 1st we've created and background. Paint with the same brush, change only the background and foreground colors.