Please help me explain 'race' to ds

[SixImpossible]

How do I explain 'mixed-race' to a dark-skinned child of white parents?

Ds accepts that people originally from different countries can look different, but doesn't understand why some who are actually lighter-skinned than him are considered (or consider themselves) black or mixed-race, while he is not.

Forgot to say that ds is 7.

I thought dual heritage was the correct phraseology so perhaps that would be easier to explain.

Otherwise if he is coming home from school asking why he is 'white' and yet darker skinned than other children who are 'mixed race' Then say that everyone comes in all shapes and sizes and some skin tones are darker and paler than others.

I have no idea what the 'correct' wording is, but if people choose to describe themselves as mixed-race, then I don't see why I should not respect that. Dual heritage is, IMO, confusing, as we consider ourselves dual heritage (dh and I come from different religions and cultures, but are both 'white').

As ds pointed out, 'black' and 'white' are stupid definitions, as we are none of us black or white. If it's about skin-colour, then why isn't he 'mixed-race', and if it's about heritage, then why can't a person with dual black and white heritage choose how they define themselves, just as we chose how we define our family?