Hello! I hope this question is not to stupid, it’s my first time working with metal!

I am doing soldering for the first time. On the left you see the chain link without soldering, on the right the soldered one.

After soldering I throw my piece I a pickling solution for 10 minutes. I use picklean.

I also hammered the right chain link as I read that makes the metal harder.

Why do the soldered pieces look so mate and grey?

What can I do? I tried sanding the pieces with sanding paper but they get even greyer. Any advice?

I am only showing one chain link, as I am a little embarrassed about the soldering joints. They are far from perfect (Secretly I am pretty proud of the thought :-))