Addressing chocolate brown envelopes?

So, my wedding colors were chocolate brown and teal, and in this vein, my stationary has all matched. The trouble I’m having now is with my thank you notes. Since the invitations were brown in teal envelopes, I’m doing teal thank you notes in dark brown envelopes. But dark brown is awfully hard to write on.

I thought about addressing them with ultra-fine tip silver Sharpie® markers, but evidently Sharpie doesn’t even /make/ an ultra-fine tip silver marker. I’ve tried frosted address labels, too, but they’re hard to read.

Does anybody have any suggestions for addressing these dark brown envelopes? I’ll buy something if I have to, I just need to get these goofy things in the mail!