Reason for tulip colour change?

Last year I planted some Bleu Aimable bulbs. The flowers that came up was what I expected – pale purple but one colour throughout. However there was one flower that was significantly darker so I thought it may have been a random bulb of a different type (first photos).

This year the flowers that came up have much more variegated petals (second photo). I love it and will not complain if it comes up again next year. Does anyone know why this has happened? Would love to know the reasoning behind this.