Ten years ago I posted this same subject on a similar forum and was loudly boo'd off. It was illegal then and still is now. We used red dye in our tractors and occasionally in the lil D50's on the farm.
I went to a horse auction in Kalispell a few years back, found everyone putting locking caps on their tanks, while they were in the sheds. When we came out, the MHP had everyone open their caps and dipped their tanks. The fines started at $1000 and went up from there.
It takes seven full tanks of D1 or D2 to flush the dye from the system.