[Cronos]

That's the thing - "race" is determined by genetics and by bone and other physical structure, not by skin tone.

By genetics black skinned Tamils and pale freckled Irishmen are the same "race"

Also note that Brits are not only "celtic" descended.

The Celts came to the British only around 500 BC. Before that, there were non-Caucasian, non-Indo-European peoples living in the isles (notably the builders of Stonehenge ) who had dark skin and blue eyes - like Cheddar man

[LouieFisk]

“Before that, there were non-Caucasian, non-Indo-European peoples living in the isles”
—
You have some sources/background info on that?

[LouieFisk]

I searched your image and came up with these articles (and a few more like them)-

DNA suggests 10,000-year-old Brit had dark skin, blue eyes
http://www.startribune.com/dna-suggests-10-000-year-old-brit-had-dark-skin-blue-eyes/473112813

Study: Aegean farmers replaced hunters of ancient Britain
https://apnews.com/a711c89f6fc8471ba0a117b2b315eacf

Though, I’m not sure you can extrapolate grand a racial movement from such singular or limited remain finds.