I’m not sure about finding a solder that is actually copper colored.
There are other Ganoksin-ers here that could inform you of that, but
I do have a “trick” to share that may be useful to you:
When I need to hide solder seems on my copper pieces, I put them in
a container of old pickle (heavily discolored blue from the suspended
copper in the solution) and I also throw in a piece of heavy steel
wool. I let them sit together in the solution for a few hours. The
chemical reaction of the steel causes the copper in the solution to
thinly plate the silver-soldered seams on the copper piece. The piece
can then be cleaned and polished or a patina applied as usual. I have
not had any solder seems pop back out and be made visible yet.
I got this bright idea after learning the hard way as a student that
one can NOT use the cheap steel tweezers to either pick their work
OUT of the pickle pot, or place newly soldered work INTO the pickle
without causing copper plating to adhere onto your precious sterling
assignment! (The poor beginner who had plated my almost completed
sterling and gold piece got the brunt of my anger as I flew off at
the mouth; I made her cry! I then had to apologize profusely for
hurting her feelings and explain the reaction when steel hits the
pickle.) But it DID give me the idea to purposefully use this
reaction to my benefit, and hide solder seams on fabricated copper
work. (I don’t like the looks of that, either) In many cases, it
tends to break up the look of a solid copper piece. My professor said
this was considered acceptable in metalsmithing, as there was no way
to eliminate this. I found a way to hide it instead.
Anyway, I thought this might be a useful tip if you are trying to
hide your silver solder seems on your copper work.