A spider as yellow as an iris

On my search for a tiny object D. first pointed me to two lice, fighting for some reason. She then noticed this spider, completely yellow. Never saw a yellow spider before. It probably was a Flower Crab Spider (Misumena vatia).
It was eating a louse and perhaps this alarmed another one. At least to our great surprise it climbed up to the spider and even on its legs.

For a white version of the same spider (perhaps even the same one, as they can change their colour!!!) see here.