The client wished for the salamander to have his likeness. He is considerably more fair-skinned then the salamander turned out.
That aside, I personally dislike the retconned notion that salamanders have onyx skin.
From the beginning, they had dark skin and faint glowing eyes. What made them special in the eyes of the imperium was not their complexion but rather their eyes.
So you actually had a chapter that weren't all white/Caucasian.
Why change that?
That seems wrong on so many levels.
So yes, I make Salamanders Dark skinned. West-Indian, Afro-American or straight out African.
I find that not only nicer, more true to how the world of warhammer 40k would look (considering dark skin is actually a dominant genetic trait, whereas fair skin is regressive. So it would be more likely that no Caucasians would be in space, some +30000 years into the future...
But yeah, if I get commissioned to paint a salamander with onyx skin, that's what I do. In this case I wasn't
While Games Workshop does try admirably, I still think they could bring in a bit more variety in terms of the cultures in the Imperium. However, since the 40k universe is so gigantic, any writer could do it, as long as it fits in with the general theme of 40k. Dan Abnett, for example, has the Tanith. He brought in a culture different from the generic ones of the Imperium, and in the process created one of the coolest Guard regiments in existence. I'm sure future Black Library books will bring in more diversity as time goes on. Keep up the good work.