How do Spanish people avoid using the word negro?

They have no need to avoid it - why should they? By saying the word 'black', which is 'negro' in Spanish, they would not be considered racist - would you be considered racist if you say 'my car is black' in English?

Yes, you would. Blackboards are called chalkboards.

Yes, you would. Blackboards are called chalkboards.

Maybe they should be called 'slateboards' though they probably aren't made of slate these days.

Or, maybe, given they are invariably both black and a board, the normal word 'blackboard', used with no intent to refer to human beings in any way, let alone as a racist epithet, is perfectly acceptable, and authoritative regressive liberal views can be safely ignored?

It's odd how we never hear anyone complain of the term 'whiteboard' as being in any way derogatory to any human group, isn't it?

But we Marxo-Liberal Feminists also like to mess with your minds and get you all red faced, so there's that.