I would have previously said no BUT just yesterday, a florist in our local market was selling some standard patio roses in tubs and they had both yellow AND pink flowers on them.

Yes. A good example is a variety that is a "sport" (a genetic mutation) of another variety such as the peach-pink patio rose Sweet Dream. It's yellow sport Sweet Memories occasionally produces a flower thats split down the middle, half peach-pink, half yellow with even more rarely, a single coloured flower opposing all the others on the plant. There are several other examples of this such as Zepherine Drouhin with it's paler pink sport Kathleen Harrop.