Well, one time I kept a caterpillar as my pet. It was green and black. It may be a Forest Tent Caterpillar.
Type your answer here... swallowtail
Many caterpillars have a base color of '"lime green" - for instance the common tomato caterpillar is all lime green. The black swallowtail butterfly's caterpillar is lime green with black and a bit...
err... black shrek?
You get dark green. Add too much and you get black.