Two-tone tulips aren't really that unusual, but they are usually intermingled with with the two colours, i.e. spots, stripes swirls, etc. What makes yours interesting and unusual, particularly the one in the middle, is the way that the two different colours are so pronounced and separated onto each side.

Is this the first year that they have bloomed Alan, and where did you get them from?

probally a genetic mutation or that one of the flowers with red and yellow in the middle mixed with a yellow flower,but the great thing is that you will have that flower bloom year after year :)

I would be tempted to contact one of the large plant and seed companies and send them the photo. I know that Thompson & Morgan are always looking for new plants and will pay you handsomely for a new discovery. Usually a percentage in the form of a royalty from how many they sell. Worth a go, you never know Alan. :o)

there is no guarantee that it will do the same next year. I had something similar a few years ago and it hasn't happened since. Its a genetic blip during the formation of the flower bud.