A gray green with no clear source
The toad on this site is #748D70, a muted gray green. This code comes from an open list of color names gathered online. No older source for it is given.
A different toad on Wikipedia
Wikipedia's alphabetical list of colors has a toad too, but it is #8B7D6B, a grayish brown. That is the same code as bisque4, a darker form of bisque in the X11 color names. It does not match the green toad here.
For greens near this one, see camouflage green and laurel green.

