It's a sport. Many roses will have flowers of a different color now and then. I have a Roseberry Blanket that has sported light pink on a few canes for 2 years now. I'm going to try to propagate it.

I've had white and half white flowers on roses, clematis and azaleas. Usually in cooler weather.

Yes, it's a sport. During the forming of the bud something caused a small genetic mutation to occur and the resulting bloom is two colors instead of one. This type of sport is rarely stable and can't be propagated. Some sports that happen can be because the genetic mutation is further up the line. If you take a cutting of the sporting cane and root it and it reproduces the different bloom then it is a stable sport and a new variety. Sports happen more frequently than you think and have resulted in many new varieties. Keep watching your roses and you'll find other examples I'm sure.

It is rare but there are some plant varieties that are twin colored .I owned one myself but there are seeds for sale online for bicolor half and half roses .I purchased seeds but it is difficult to germinate as i discovered later

This thread is 11 years old. it looks like the OP's rose is maybe a Brilliant Pink Iceberg that has partially sported back to Iceberg. This is really common with BPI, and also Burgundy Iceberg. Seeds purchased to achieve this will most likely not produce what you want.