I did this as a tutorial on a make up bruise, but I think it can be applied on how to draw one as well!
I cut out all the text tho, since it was all about make up.

1) Start off with a darker base color
2) Dapple yellow around the edges and give a few blue blobs in the middle (not dead middle, just be random!) Make sure to blend the colors a bit.
3) Stipple red across bruise.

4) this is mostly a make up step but-- if you wanted, go over the entire bruise lightly with the base color from step 1. it helps blend everything together.

FOR A MORE HEALING BRUISE.
-Start off with a lighter base color
-Instead of blue, use green (plus the yellow)

Looking at actual bruises will help! and different colors for the different healing stages.
I recommend actually looking a MAKE UP videos on making a bruise, it can help you as well!

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