I tend to think a lot of this discussion of the correct color for mayfly bodies (and in particular for the sulfur, or at least that #16 sulfur that produces such significant hatches on PA streams) is as much based in religion or what we have experience/faith in as it is in anything having to do with reality or actual imitation. You can sort of see it in the fairly wide variations of body colors recommended on this thread.
Given that, here's what my religion tells me about the "right" color for sulfur duns: For the body, I like to use a mix of dubbing that is close to a medium, sort of dull tan with a bit of a yellow highlight. I'll take out my standard tan dubbing and my bags of bright yellow and pale/dirty yellow and keep mixing them until the result is what the voices in my head say it should be. Usually, it ends up looking a lot like what the voices in my head told it me it should look like when I was tying sulfurs the year before.
In religion, this is what we call receiving a sign...
Whatever it is though, its way more tan than yellow.
The nymphs are (again, according to my religion) somewhat different. I do best on sulfur nymphs that are more of a camel color than either tan or yellow and a little bit fatter in the body than you might make the normal nymph. Well, maybe camel with a little extra yellow in it. I tie them on a #14 wet fly hook because: 1) this seems to be the right size and 2) I have a lot of #14 wet fly hooks left over from the time I decided to bypass all this caddis pupa crap for the Grannom and just fish a Leadwing Coachman. Which worked well enough to suit me and the voices.
Troutbert has told me a number of times that a pretty effective sulfur nymph can be made of equal parts medium hare's ear and regular yellow mixed.
I ran this by the voices in my head and they said it was a sound idea. And so I made some and they worked pretty well.
This made me wonder if the voices in my head weren't really Troutbert. But I don't think they are because they have yet to say anything to me about the importance of woody debris...
That's all..