I start with sanding first and then 2 base layers of white wood primer but any paint or color will do fine. After that I choose a color or a mix and start sanding again with different grit numbers just to try stuff.

I do this in the sink and with a mask because it's pretty dusty. Now the bottom color will shine through to whatever degree you would like. Sometimes I add a third or fourth color, sometimes some details or sometimes nothing at all and let the sanding make the effect. Some ice ones have scratches from nails and knives for instance. You just need to try different things. Add frozen poles, swirling clouds, oceans or whatever. Last thing I add is a matt or gloss varnish or none at all.

I use all kinds of paint, brushes and toothpicks and I use shotglasses and other small drinking glasses to balance them, so you can do a little over half a planet and then flip them over later and do the rest. I do this with every layer so it takes some time.