Metal Compounds + Aerosol (plus some halogens and chalcogens)
Aerosols have an extremely good advantage in which they can remain airborne for a really, really long time.
Metal dust cannot float on its own, it will sink down due to gravity. However, by binding them to an aerosol like certain CFC compounds, they can float in the air.
It also doesn't have to be metallic compounds. It can be done by non-metals as well.
So the order would be:
Red- Iron oxide
Orange- Crocoite (Lead chromate)
Yellow- Sulfur particles
Green- Chlorine gas
Blue- cobalt(II) aluminate (CoAl2O4)
Indigo- Powdered hydrated copper sulphate
Violet- NH4MnP2O7 (ammonium manganese(III) pyrophosphate)
Many of these compounds are really hard to synthesize using modern-day tech, but heck yeah, your civilization have godlike technology, so creating such a grand artwork would be a petty thing for such a civilization.
TL;DR Attach a bunch of metallic compounds to an aerosol and spray them over the planet in bands. The particles will be carried around by the winds to give it a distinct colour for each band.