Doubtful that's the cause - sometimes plants don't hold their vivid colours longer than a year, they're all hybrids and bred to within an inch of their lives, and colour reversion is not uncommon even in roses - peach turning to pink being a prime example.

Either that or the originals have died and been replaced by the wishy washy pink which you get when you cross the yellow primrose with the red Primula

Thank you for your help