If you happen to see a Comma butterfly on one of our fine autumnal days, have a good look at the colour of its wings. You may notice that both the upper and the undersides of its wings are quite dark, particularly when compared to some of the Commas you saw in the summer months. Why is that?
It may be that your paler summertime Comma was a hutchinsoni. The splendid Life Cycles of British & Irish Butterflies explains:
The Comma is known for a particular form named hutchinsoni that is much paler in appearance on both upperside and underside that the nominate form. This form is found throughout the butterfly’s range and is normally attributed to individuals that go on to produce a second brood in the same year. Its name is a tribute to Emma Hutchinson, a renowned Victorian entomologist … who ultimately discovered its double-brooded nature and the corresponding variation between broods. The name was announced by J.E. Robson in 1881 in The Young Naturalist: ‘The Summer form is so different, and so constant in its appearance, that it ought to have a distinctive name, and we suggest it be called var. Hutchinsoni, in compliment to the lady … whose knowledge of the species is not exceeded by that of any one living.’
In my photos, the Comma on the left, Polygonia c-album var. hutchinsoni, was photographed on 24 June, the Comma on the right on 17 September, both in the same location and on fine, sunny days. I think you can see how marked the difference in their colouring is.