Hello everyone.

I have a few things to ask regarding vocal melodies. I don't sing (yet) myself but I was wondering:

Considering the key of your vocal melody, how hard is it to add some chromatic elements to your melody? It sounds like it could be really unsettling.

Also, is it common practice to have a different key for your vocal melody and the other instrements? That looks like it would be confusing to the singer's ears.

I tried looking it up, but looking for things like "key, chromatism/c, vocal melody" didn't yield anything.

Thanks ahead of time
honestly, if you play guitar (and I think you do) and have a basic understanding of theory, look into some jazz concepts about use of chromatics. I will show you when to use the "wrongnote"at the right time.

Also if you make up a melody,play it on the guitar and try to experiment using chromaticism via trial and error if all else fails. You would be surprised how well it can work.
I understand chromatism can be useful.

I'm more wondering about that applied to a vocal melody and the way it can interfere with the other instruments in a band (potential different keys?).

Maybe this is a "not enough experience" situation, but I've been told about how mood might affect one's ability to sing in a major/minor key. That kind of stuff.
If you can pitch notes in your head (as you should be doing when you're singing), the only thing holding you back from singing incredibly dissonant and chromatic notes is a case of practicing parts that are tricky. If the notes are singable by the particular vocalist, then it shouldn't matter - it might be tough, but if it sounds good then it is definitely worth just putting some time into it.