The pink AMEX is one of the most popular nymph patterns in winter and early spring on the Missouri River, and a good bet on any tailwater stream. It suggests both eggs and dead/dying scuds, and as such is a good “junk bug” attractor pattern on tailwaters.
While normally tied on a scud hook, I prefer to tie larger versions (#12-14) on jig hooks with tungsten beads, to cut down on hangups.
It’s also worth checking out the “Rainbow Czech,” which is generally similar except with the dubbing colors reversed and a full scud-style shellback. Both patterns bear some similarity to the Pink Squirrel nymph popular in the Driftless region of the upper Midwest.
Full recipe at Walter’s blog at https://fishstories.ycflyfishing.com/