I mean the brush or the layer is set on Overlay to make the effect look like it's on the apple. But this removes the bright highlight dot because white on overlay just brightens an area up instead of keeping the white. So the highlight has to be added separately on a different layer so you can see the white highlight.

I understand, thanks David Wood.

of course, one easy way to get the highlights back would be this: duplicate the drops layer once you've painted in all your drops with the brush. then you can set the bottom layer to overlay and keep the top one at normal and on the top one you do a colour to alpha to take away the black, leaving only the white highlights.

Yes, I think that would work well too.
I was going to add more highlights to the animated brush, but I don't think it would do much good.