^^That is the exact ones I have, black, etoupe, barenia birkins
Etoupe is a great neutral bag!! If you are deciding between your SO and etoupe, then I say wait for your SO because your other bags are pretty neutral already. But if you are thinking of something else besides your SO, then etoupe is a great choice!!!
My "dream bags" are birkins in black, etoupe and natural barenia (I also love tabac camel but the colour doesn't love me back) so I think that etoupe would be a perfect addition to your collection. Your tabac camel and natural barenia birkins are both 30 cm so I would wait for an etoupe 35 cm birkin.
I have etoupe and tabac camel and I think they are not too similar...Hmm, it is a little close to tabac-camel, but if you do use them regularly, why not?