Gel or paste color definite. For one, dust is more expensive and that's why it's usually used, most times, only as highlights as against actual painting. Secondly, the picture has different shades of black which shows as grey where it is lighter. You can best achieve this through use of paste/gel. With this type of job, there are going to to be wiping and cleaning as corrections only to repaint, colors are best for this. The dust may come later to brighten the completed work.