[header] How to paint circles [title] Choose your graphite. [step] A very light shade of graphite is ideal to prevent the marks from showing through your paint. This is especially important if you paint with watercolours or other thin paint, which requires a 6h pencil or an even paler option. 
[substeps] It's okay to have faint pencil lines showing through watercolour, as long as they aren't too obvious. Some artists even use this intentionally, sketching in pencil then applying a very thin wash of paint over it.