Joshua, this is hard to discuss/give examples on, online. One reason is that muddiness doesn't always show in photo images. I once had a daylily seedling which from its picture had fabulous color, but in real life it was muddy as heck. You have to see the blooms in real life.
That said...from my earlier post compare AGAIN AND AGAIN vs LUMINOSITY. The former (at least the falls) looks muddy to me (because there is a hint of blue or purple or something which dirties the yellow color), whereas the latter is, well, luminous in color, not dirty (aka muddy). It's some shade of yellow and nothing but (or at least, the yellow overpowers the mud from any other color
).
This summer, I noticed that the falls on EMMA'S LAUGHTER had some coloration in them. Compared to NORDICA or COZY COTTON, the falls look muddy to me. (That bit of greenish/creamish color might be attractive to some, but every time I looked at it, I thought "mud". It was color that in a perfect white (or blue-white) self would not have been in there.)
Do not confuse a lack of color intensity or saturation (or vice versa) with mud (or a lack thereof). A pale iris can be clean or muddy. A strongly colored iris can be clean or muddy.
The best verbal description that I can think of (for discerning muddy from not) would be something along the lines of, look at the bloom as though the standard/falls were made of a colored or tinted glass or crystal. Is that an appealing gem-like glass, or does that glass look like it is in need of a wash? (Don't let diamond dusting confuse the issue. While appealing in and of itself, that has nothing to do with clarity of color.)
I am uncertain (I have seen very few of them (1 for certain)), but it may be the case that the glaciatas are among those irises with the cleanest color. (This isn't to say that blue or lavender or purple irises can't have clarity.)
I had a NOID iris bloom this past season. The form is unexciting, but I am considering keeping that iris anyway because it had very clean color. (Image below - you can't really tell from the photo that the color is clean, but it is.)
Sorry if this is not helpful. As I think I may have said earlier, flower color clarity is something that is hard to grasp until/unless you've experienced it.
You have to look at a lot of irises (daylilies) to find the (relatively rare) ones with great clarity of color. Once you've seen such a bloom, then your eye/brain goes AHA! and from then on at least the really muddy blooms will be easily apparent to you.
(Fwiw, in the daylily world, if you are hybridizing and want to clean up the mud in a flower, you typically cross it against the cleanest near-white or pink or purple daylily that you can get your hands on (ideally the pink or purple is known to throw near-white offspring). You would also most likely use the cleaner parent as the pod parent, because a lot (all?) of the time, the muddy color is coming from pigments in the underlying (beneath the color layer) tissue, and as I understand it, that is maternally determined. (This is also why the diploid near-white daylilies are whiter than the tetraploid ones, because the tetraploid daylilies have thicker tepal tissue.) But that's daylilies. Color determination seems to me to be a WHOLE lot more complicated in the iris world than with daylilies.
That said, I note with interest that LUMINOSITY comes from a cross between a somewhat orange-y looking yellow and a very clean looking pink (going by the pictures, and pictures can lie
). The pink, VANITY, was a Dykes Medal winner by Ben Hager, who had a foot in the daylily world and presumably knew something about clarity of color.)
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