Her color is just called black. I wouldn’t call the color specifically popular, but I don’t believe it is. If it’s worth it to buy her is mostly personal opinion you might just want to think about:
1. Fully pedigreed rabbits sell best
2. (Unless you’re buying her for personality) a black rabbit won’t really add any fun or cool looking colors or genetics to your current herd.
3. She is going to likely have mostly black babies and if she doesn’t have a pedigree you’d have no idea what other genetics she might have.
I personally wouldn’t, but it is a matter of personal preference.
To start a rabbitry I recommend researching genetics and finding a fully pedigreed rabbit with the genetics you want not just the first rabbit you can find.
Here is a link with a bunch of great info about breeding and genetics (it’s for Holland Lops, but a lot of stuff is universal).
There are other people more experienced then me on here who might be able to tell you more.
I hope this helps!