James, that is one odd looking grub! I have uncovered lots of them, especially the japanese beetle and green june beetle larvae, but never seen a green one. It is kind of cool, used to be mostly japanese beetles, now getting more june beetles which I think means my organic matter is gettting better! They are detritovores, versus the japanese beetles eating the roots.
I wonder if there is a source of copper or nickel giving that color?
Standing on the shoulders of giants. Giants with dirt under their nails
Interestingly enough Tj, there are members of the Scarabeiform family that are white, green (three or four shades of green even) and blue or azure colored.
I can't say whether or not soil mineral content has any bearing on the color of any of the larvae.