This bug had just molted, I think. You can barely see the black piece with legs nearby. The bug's body was about 1/4" long and it had really bright coloring, as you can see. What is this insect? Isn't that moss cool? It's all fuzzy and looked neat with the lichen on the trunk of this tree.
Looks like the 2nd or 3rd instar of a True Bug (Hemiptera) to me - but I'm no expert.
As gardenwife says, the nymph has just molted - it's possible that when its chitin exoskeleton hardens, the colors will become more muted.
BTW, the insect Order Hemiptera includes such cuddly critters as stinkbugs, bedbugs, assassin bugs, and the especially adorable one in the Andes that spreads Chagas disease. Here's a link with some other colorful examples: