sometimes switching between rusty's that have different wing types can be the difference. Poly yarn wings are easiest to see in low light situations ,but when they are being tough hackled wing rusty's tend to work a little better. If its getting dark and they are still being selective, Ill fish a bigger white cdc sulpher and tie a sparse winged rusty spinner off the back(15 inches or so). It works really well and you sometimes get surprised when they take the bigger fly. In terms of color, I dont think it matters that much during the late evening spinner falls ,but have seen them get pickier during the day. Having darker maroon spinners and lighter pinkish spinners can work in certain situations. S[ent wing caddis are also a clutch pattern to have in tougher conditions.