The Timelords have spent the last million years indoors.
Everyone on Earth used to be black, it's only taken a few tens of thousands of years for roughly the same looking ethnicity to divide into what we regard now as a typical strata of human diversity.
And %99 percent of those tens of thousands of years, we as a species had mostly spent outdoors.
English weather makes white people.
If you want to chose, decree what colour your family will be graduating towards for the next thousand years, move and plant your legacy where the sunlight will reflect that aspiration, baring of course any catastrophic climate shift.
So saying all that, what I found ridiculous was all the lilly white anglosaxon cavemen in The Savages.
How many Asian actors were in Marco Polo?