Brown is a colour, white is a colour, black is a colour. They have tones/shades and I do not relate them to the individual, the person I suppose when purchasing bras, perhaps I should. However where does it stop and end?
Somebody with Rosecca could decide a bra called Strawberry/Red Flush should be renamed as they equally find upset by it's description and ask for an apology, after all the colour of our skin is individual to us all it is not the domain of only one homogeneous group/race. See that comment as a throw away as you may but if there is a genuine concern for how individuals of all skin types/colours feel then it is perfectly a reasonable point to make. If only one skin type/colour is to be spoken of then that points to where the debate by some wish it to stay.
White/Black however by their nature are not given to a wide varience in shading but brown is.
Did the M&S merchandising team look at their brown range of bras and conscientiously decide they were only for women of that colour to purchase or a brown range of bras for All women to purchase? If the range was produced and marketed as a range for women of a specific colour then I suppose the descriptive name matters.
Was the brown bra range produced and merchandised purely as a range of brown coloured bras for the general population I see absolutely no offence in the description Tobacco Coloured.