The coastal cutts that lived their entire lives in places like beaver ponds certainly took on different coloring from what I remember. I can recall catching some that had almost brown backs with yellowish / orange bellies. This of course was years ago.

Here are some cutthroat pictures.
The first three pictures are some saltwater cutthroat from the past few years that show the variation in colors. You can see the yellow color forming on the lower jaw and belly in the second picture.
The last picture is from a stream that does have beaver ponds on it.
SF