We humans just want everything to fit in nice tidy little boxes.
Guess what, the world is not one of absolutes, it's one of generalizations. We use generalizations to guide our thinking. There will always be those individual irises that push the envelop one way or another. I wonder if at the time the term "neglecta" was coined, there were very few colors in irises. So it was a handy term for those purple and blue ones with standards that had a lighter tint of the same color. Then comes the progress by hybridizer's, and low and behold we have reds and pinks and oranges and they have lighter tints of the color of the falls, but since we had our minds locked into neglecta only being in the purple and blue range, they began to call them bi-tones. Guess what a neglecta is a bi-tone too! I for one think the term Neglecta is outdated and of no use any longer. It served it's purpose but I believe it's time to move on and just call them Bi-tones and be done with it. The term amoena should be used to categorize those with pure white standards that do not have color washed in them. But knowing how change is pretty much impossible I'm guessing 500 years from now the same dialogue will be going on.
IMVHO