I think the more vivid yellow tinting is partially diet and the lack of darker pigmentation. The lack of darker pigmentation is likely due to sexual immaturity and the pictures being taken outside of the spawn. I fully expect my larger, sexually mature dominant RES to darken up quite a bit in late May and June. IMO the lack of darker pigmentation also affects the appearance of the ear tab coloration as well making it appear more orange than red in males, "tweeners" as TJ likes to call them.
I am going to focus on taking pictures of 7"+ fish as we get closer to the spawn to focus on more sexually mature fish. One thing I have noticed taking pictures of the urogenital openings is that there may be some slight, but noticeable differences in the length of the pelvic fins when laid flat against the body that might be gender specific.
