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From Arnold 5, the UVs on hair are the skin UVs. You can use the barycentric coordinates to get the per stand UVs, in your case that would be "bv" from the state_float shader.
Great, it Works! Thanks a bunch, Buddy. For others: In Arnold Hair shader ad "State Float" choose "bv" plug StateFloat to a ramp (texture) input and change "Pattern" on Ramp to Custom.