The upholstery in my 1941 is brown. I have not seen one with original black upholstery, but I haven't seen all of them.
I couldn't find correct replacement seat covers from the parts places; the piping on the bottom cushion was in the wrong place. Also, the reupolstery kits come with a piece of carpet underlayment for under the bottom cushion cotton padding where horsehair was originally used.
Here is what my original seat looks like:
Click Interestingly, Alkay's 1940 shows some original interior details which are usually overlooked during restoration: The inside firewall is painted interior color, and the headliner and kick panels are painted interier color instead of dark brown like the reproductions.