Black dog turning brown

Hiya!

Does anyone know any reasons as to why my black dog has a brown undertone?
I have researched far and wide. I have read it could be the sun bleaching, however even now in winter he still has a brown tinge, I brush him everyday to get rid of dead fur (he has part doodle in him). He always looks 'black' but in the light he just has an all over slight brownish tinge. I rehomed him when he was 10 months and his previous owners said he developed it around 5 months old. I also feed him a raw diet and give him fruit and veg and extra supplements, so I was wondering whether I could be missing out on some other supplements?
I've just been putting it down to genes at the moment but if anyone else might know the cause it would be helpful, thanks!

 

Thanks judy, not particularly, the lower part of his back is a lot coarser, but I have found that happens with other dogs, but the rest of his coat is nice and healthy must be in the genes!

 

Thank you! I was thinking maybe omega 3 oil to see if that might improve it. His general health is fine, and his skin is healthy, so may just be a brown hue