Is this unusual? Only 2 roses are duel color so far - white iceberg bush is about 8 ft from the burgundy one. Both are about 10 years old. This has never happened before with these or any of my roses. So curious

Its a chimera - where 2 sets of DNA come together in one flower or leaf (or animal). Variegated plants, multi-colored animals, they're all spontaneous chimeras caused by a mutation in the genetics of the plant (or animal). Some are permanent and some are fleeting, like your roses - it may never happen again. What makes your rose interesting is everything I read about spontaneous chimeraism in roses was either a white iceberg or burgundy iceberg rose.

I have a Japanese flowering quince that every few years, has a few red flowers scattered amongst the usually white/pink flowers. This is the year.

Yes, it's common in color sports (mutations). If you look at the photos of Careless Love on Help Me Find-Roses, you will find several where Careless Love is sporting to Mrs. Charles Bell, the light pink mutation of Radiance. I've observed it on Mary Rose a number of other roses which have sported to other colors, or reverted from them back to the original color. Decades ago, I imported Great News from LeGrice in Britain. It was a dark "pansy purple with silvery reverse" floribunda. It threw a cluster of blooms where the central bloom was half pansy purple and half lavender. The blooms on the purple side were the original dark purple while those on the lavender side were all lavender. I isolated it and grew it for some years, even registering it as Great News Sport. Yes, it does happen, not all the time but sufficient enough to be known.

It's also still very cool!

My Burgundy Iceberg does that from time to time. It's interesting that my Brilliant Pink Iceberg never has.
My Hocus Pocus bushes have sported back and forth all over the place. The most typical is for it to revert to Black Beauty and stay there, but I've had BB sport back to HP. Once I had a bush with HP, BB, and the original parent Frisco all on the same bush. I'm keeping my fingers crossed that Alakazam and Simsalabim don't sport back, since they're extremely attractive, unique, and hard to find. (All of those are sports in the same family).
Last year, my Sunset Celebration produced one bloom that was 1/3 dark pink, which has never happened in the 20+ years I'd been growing various plants of it. Sports happen!

My Young Lycidas did the same thing once, but it didn't happen again.

5 days later.

#1 Here's my Sunset Celebration sport from last year. Like Aerith's, it hasn't done it again (yet). #2 Abracadabra that has never bloomed striped, but last year produced a half and half, and a full Frisco (yellow) bloom. #3 & #4 Alakazam and Simsalabim, further sports of the original line that so far have been stable for the 2-3 years I've had them