Sorry about the cover photo - this post was inspired by seeing the Unbrave Two in full sunlight. Their wing feathers shone violet. And I thought about how they likely see ultra violet light and it may be that males and female have distinctive patterns and do not look the same to each other.
I am sure they are not the same anyway - I think that females seem to have slightly smaller heads. That seems true of Droopy and Diva when compared to Three and Divo.
Still, the crows and the squirrels are not exactly brilliantly coloured from my point of view - and I don't see the foxes in daylight or get a good glimpse of the goldfinches. It's no wonder we love robins so much - for most of us that's all the colour we see... once the leaves have fallen.
For now, the leaves are still turning.
On the roads, where there are a mixture of species banking the tarmac, it's already stunning - with some glowing yellow, orange, red and others still busy making the most of the sunshine with their chlorophyll.
Many love this time of year. I find it challenging. The turning unsettles me and I feel a melancholy for the loss of warmth and the coming darkness.
YES, I often admire the purple-black colour in sunlight. I like your supposing about U.V. and also female's smaller heads. I'll watch for that. A lot of our (American) Robins leave in the fall but we seem to be getting more Cardinals in the winter on PEI and they are VERY colourful :-) https://www.youtube.com/watch?v=mevWgPIIVhc
p.s. Yes, I have mixed feelings about autumn too.