Some call them 'blooms' others refer to them as 'cauliflowers'.
Okay, I've already done a blog post on this, but since it is a recurring issue with artists, especially those first learning, I felt it was worth another post here.
In this example painting of a Lighthouse, you'll notice that there is a darker area representing a window on the body of the building. I did this Whilst the other paint was WET, and yet it didn't spread > bloom > cauliflower.
This was possible because when I added the window, I used a thicker consistency of paint, thus the weight of the paint being added was heavier than the paint it was going into, and hence it didn't spread.
~ I hope this blog post is of help ~