It will catch fish!
It appears the fly has big "doll" type eyes? If it were me, I'd drop those. Hellgrammites don't have such big eyes. As for colors, if you look at helgy nymphs, they tend to run 2-3" in length and are brown/olive with dark brown/black heads and thorax. A good ratio would be 2" of olive body and 1" of black at the head. Helgy flies are often tied in all black or with black bodies and, although they catch fish, such flies don't match well the color pattern typical of our helgy nymphs here in PA. Olive marabou is tough to beat. Dislodged helgy nymphs swim with an undulating wiggle motion (so do craneflies but that's another thread) so a long marabou tail really works well.