Please could someone tell us if there is such a thing? My friend was talking the other day about seeing a Boxer litter and there was a black one!!!

Yes, they happen occasionally - I've seen photos! They're classed as a mismark and are certainly not worth more than standard colours.
:)

I think they are called 'reverse brindle' and are actually a VERY dark brindle
Archer

It's funny this thread has turned up at our ringcraft class on Wednesday i seen a very dark brindle boxer pup, can they still show them if they are very dark brindle?

Warm regards Susan

Yes but the UK breed standard clearly stipulates that the colour brindle is
black stripes on the base colour which is various shades from dark red to light fawn.

Yes the dark brindles can look smart, but solid black colouring is considered a 'fault'.
In the US they do allow for the 'reverse' brindle colouring but technically here they should not
but I don't think it is penalised as heavily here in the show ring as it could be.