I don’t know of an animated effect to do this. I did it once by shooting real paint on a piece of clear glass in front of the video camera. I used a dark paint with the camera aimed at a white wall. Thin the paint so it dribbles. Thicker paint makes nice splatters.
Use a turkey baster to get a more forceful splatter. Do a few takes and key them to be the color you need. Loads of fun when you have kids around to do it for you!