Heartsease diptych

Viola tricolor is a European wild flower the progenitor of the cultivated Pansy, an infusion of the plant was said to help mend a broken heart, hence its common name Heartsease.
We've always had a lot of Heartsease that have randomly re-seeded themselves throughout the garden, they are really tough for such a delicate looking flower. The great majority have always been the hue of the flower on the right but every year there are some plants which display some colour variation. This year we have been luckily enough to see the really dark Heartsease on the left, it is almost black and I can't remember seeing one this dark previously. I will hopefully be able to collect seed but there's no guarantee what colour the resultant flower will be.