An image showing how to create a photorealistic effect using only the hard round brush and opacity - no pressure sensitivity, no colour picking. I did this in the dead basic graffiti drawing app, so could be recreated with most other programs.
Actually I should have taken one more screenshot at the very beginning because getting the right base colour is crucial. I started with a solid all over grey, judged the general tone by eye from my reference photo, then overlaid the separate areas with very low opacity large brush strokes in peaches, purples and green etc. to get that varied grey/beige base.