Light fitting with American coloured wiring but bought in UK
How do I know that this is either meets UK electrical standards and can actually work with a 240V mains circuit? The only documentation that claims this is the case is in the Amazon product description


You don't. It probably does not (meet the standards - working on 240V is easy enough), or it would be so marked. 

Heck, the vendor didn't even bother to put on counterfeit certifications (which are a bit too common for comfort.)

I would suggest returning it for that reason. Who knows how badly it's made?