I grabbed a scanner recently, and part of the plan for future art is to seperately paint skyboxes and distant backgrounds since my colored markers struggle with large areas.

This is just a compositing test using the first suitable picture. I painted a spacey background and scanned it, then opening the scan and drawing in GIMP I put the two together. I did some mild color tweaking of the background to draw out color, darkened the black of the spacegun, and then at the end added a tiny bit of color noise to visually bring the layers together.

Original drawing:

Painting:

Composite without visual noise: