I have tried yellow and found them ok to a point. Then I took to dipping the yellow post tip into orange fluro model paint before trimming to length and that worked well after a bit of teasing with a dubbing needle to unstick the fibers a little.
Also tried adding some strands of glothread into the poly and that didn't really work well as I hadn't charged the glothread before I fished it

. I lost that fly in a tree and haven't tried the glo since but may do again.
Maybe dipping in glow in the dark paint would work well. Must try that! After halloween is a great time to pick up bottles of glow in the dark nail varnish, perfect for painting rod tips, floats etc for night fishing. Also handy if you want some glohead flies.
Now using some bright pink 100% artificial fiber knitting wool. Got a massive ball of it for £1 and there is enough to make thousands of flies. It is highly visable on the surface and floats well due the the way it can hold air. Also holds floatants well.