Why always in black leather ?  

I interviewed Matali Crasset ...
I interviewed Matali Crasset for The Sydney Morning Herald the other day (she's the famous French designer who once worked for Starck). She told me she never uses black, because it is too chic and elitist. And so it divides people along class lines. Plus, she thinks everybody is scared of colour.
Stephen

Everyone IS scared of color...
So few know how to orchestrate color to please and, as a result, so many have had their eyes assaulted.

It was Hubert Givenchy that...
It was Hubert Givenchy that put Audrey Hepburn into black..but I see your point!
Black is used for showing furniture simply because it is the best seller.
As with fashion, every buyer orders black..then the colours.

talking about black...
Most forum contributors seem to consider the empty chair and how it works in an interior. If I would choose black it would be for the fact that it shows off the person that sits in it...
Personally I like leather a shade darker than the normal FLW-red, but it would require a very dark wood for the structure (wenge would do)and dark wood is not my favorite.
The point on the fear for colour is very true. Combining colours seems to be a major obstacle for many people....and so, in spite of the multitude of colours offered in the stores "the" housewares colour is still white (over 70% of sales in most products) or black when combined with chrome or other metal details.