How sure are you? I do joke a lot, but in this case...
The slave trade formally ended in Britain in 1807, and slavery was outlawed in 1833. I haven't been able to find good statistics through a cursory search, but with England's population around 10M in 1800, that 99.9% value requires less than 10k non-white Englanders kicking around in 1800. I saw a figure that indicated around 3% of Londoners were black in the 1600s, for example (a figure that doesn't count people from Asia and the middle east). Hence my request for sources, I'm genuinely curious, and somewhat suspicious that somebody would be so confident to assert 3 significant figures without evidence.
But surely you wouldn't find a black king in Britain in 1800.
I - Whatever was implemented is myopic and equals racism to white. It appears to be an universal negative prompt like "-white -european -man". Very lazy.
II - The tool shouldn't engage in morality reasoning. There are cases like historical themes where it needs to be "racist" to be accurate. If someone asks for "plantation economy in the old south" the natural thing is for it to draw black slaves.
I question the historicity of this figure. Do you have sources?