Outstanding stencil work! My first response would’ve been a bsroegsted rainbow metallic, but after studying it more, I think I’d choose one color for each motif. Jewel tones on black are my favorite!
For example, turquoise for all the large medallions in each square, for the interlocking arches, fuchsia for the flowers, and so on. I’d color it all in a rough sketch on paper first. It’ll take extra work to change, but the result would be eye-popping cool!