Or as the author of the tumblr People of Color in European Art History puts it:
"The all-white reinvention of Medieval Europe commonly depicted in popular fiction, films, tv shows and art is entirely that: a fiction. An invention. An erasure. Obviously, people of color have been an essential and integral part of European life, European art, and European literary imagination since time immemorial. To cite “historical accuracy” as a means to project whitewashed images of the past into the future to maintain a fiction of white supremacy is an unconscionable farce.
People of Color are not an anachronism."
Prehistory: As far as archaeologists can tell, different humans and human-relatives, like Neanderthals, left Africa and eventually wandered over to Europe. Different waves of people looked different, acted differently, and may not have even been Homo sapiens, but it appears that they did occasionally inter-marry. We don't know exactly what these early people looked like, but from what I've read, our best guess is that they looked like the Khoi-San peoples of southern Africa. Skeletons like those of Grimaldi man (actually two skeletons,) appear to support this idea. No one is sure when (or why) people in Europe became light-skinned--some think it was long ago, in response to the climate; others think it was much more recently, in response to agriculture. But even as some groups began looking like some modern Europeans, other groups were moving around, migrating, intermarrying, wiping people out and getting wiped out in turn.
Here's a painting from Bronze Age Crete, 2,700-1,500 BCE:
No one knows who these brave folk were, (and the painting may not have been intended to be a portrait of anyone in particular,) but clearly, the artist had met folks with more than one skin tone.
Classical times: By the time the Romans showed up, the ancestors of most of the modern European ethnic groups we know today were hanging out and interacting, and they sometimes showed up in in surprising places. For example, sub-Saharan Africans (as well as North Africans and Egyptians) lived in Roman York, (as we know from their graves). The Romans liked to mix things up by moving their soldiers and mercenaries far away from their homelands, so they'd be less likely to unite with the peasants in an uprising.
"There is evidence of the presence of black people in Roman Britain. Archaeological inscriptions suggest that most of these residents were involved with the military. However, some were in the upper echelons of society. Analysis of a skull found in a Roman grave in York indicated that it belonged to a Black African or mixed-race female. Her sarcophagus was made of stone and also contained a jet bracelet and an ivory bangle, indicating great wealth for the time." Wikipedia.
So there were black folks living in England before the Anglo-Saxon invasion.
The Mediterranean was the highway of the Classical world, and many famous folks came from places you might not expect. For example, Herodotus, of the Histories fame, was born in Turkey, and the famous Roman Christian St. Augustine was born in Africa, in what is now Algeria.
And this guy:
Terentius Neo, was a baker in Pompeii. (Sadly, his wife's name does not appear to have been preserved.)
Medieval times: In the Middle Ages, North Africans ruled Spain for hundreds of years, Arab and African merchants traded gold and spices, Roma wandered, Jews did various things, Africans were sold into slavery, ambassadors and mercenaries did their jobs, people settled and moved and intermarried, and of course there were the Magyars and Turks and Mongols and Sami and Basques and so on and so forth.
This Romani lady is being robbed.
Sami family, from far northern Europe.
Alessandro the Moor, one of the de Medicis of Italy.
Hasekura Tsunaga, the Japanese ambassador, painted in Italy in 1615 by Claude Duret.
Not to mention that ethnicity is relative--if you grew up in a small, isolated community in northern England, those folks in southern England might as well have been in a different country as far as you were concerned. They'd speak with substantially different accents, perhaps be on the other side in a civil war, might practice their religion differently, etc. But at least they're still kinda English, unlike those Irish over there, who even in the 1800s were depicted by non-Irish as subhuman. Unusual hair or eye color for one's area could really stand out, for better or worse.
And as we approach Lyta and Jasper's time, we have:
Kalmyk girl Annushka, 1767, Russia (Eastern Europe: the forgotten 2/3s).
Queen Charlotte of Great Britain and Ireland, painted by Ramsey in 1769, and
Thomas Dumas of France, painted by Oliver Pichat in 1790. (Lyta and Jasper could have met this guy.) Dumas, you say? Why yes, he is the father of that Dumas, author of the Three Musketeers:
Keep in mind, much of this goes in reverse, too. White folks showed up in places you might not expect them, either. People have always moved around.