Problem
The nature of good camouflage is to have similar colors and similar textures the frog here demonstrates this by being both grainy and practically the same color as the leaf it is sitting on.

Solution
On noting the nature of the image I was dealing with (camouflaged, similar colors) the first thing I did was up the HSL settings in the IIL tool. I found by trial and error that saturation does not affect the selection one bit; so I turned it down to 0 which made the selections much more...