I have been wanting to try this technique out for a while, I’m quite happy with how it turned out.
I created this look by using my paintbrush to apply coloured dusts with vodka in strokes in a random order darker at the bottom lighter colours at the top like a water colour painting once dry I used edible marker to draw random black shapes over the top trying to capture multiple colours in each shape attached is how cake looked before applying the edible

marker.