Like you said, Marvin, what else have we got to do. If that seedling has different parentage than the other, I would definitely try crossing the two. Even if they are sibs, it wouldn't hurt to cross them. New colors and/or patterns almost always carry with them poor form or stalk or deficiencies in hardiness or some other fault(s). Life is never that simple. If it were, turquoise irises would probably be growing wild. I am intrigued by an old Cayeux diploid blue called Floridor (which I have) which supposedly carries a blue pigment that is only found in that variety, which produces a slate blue color. I think a few people crossed it in the past and the pigment evidently carried over into seedlings. I don't think any of them ever made the transition from diploid to tetraploid though and given the appeal of a blue-grey iris, I doubt few people gave it much a try. Who knows how that pigment would react in combination with others though and since the ploidy jump could happen at any point in time, it might be worth a few attempts. It would at least be interesting to cross it with a few other blue diploids to see how it affected the color.
In reference to your yellow/blue crosses early on, I did the same thing with much the same result--God-awful muddy yellows. One cross however did give me the greenest iris I have ever seen--a nice clear solid self in a green about the shade of a Granny Smith apple. Very nice form too. The cross was It's Magic X Swing N' Sway. So how come California didn't beat a path to my doorstep? While the flower was probably the nicest green I've seen, it bloomed on a stunted, deformed stalk, deep down in the foliage. At first I thought it might be due to frost damage, since it was an early bloomer, but no. It always bloomed with the same habit. So did its seedlings unfortunately and no green in them. It hit the compost pile years ago.
