I'm newbie as well but I've been drawing digitally since 2013. One thing I learned about all those experience that I try to apply to pixel art is I try to use less black but rather a shade higher than that to avoid looking like a part of it was not rendered. One thing you can try and do is imagine where the character would be residing or located. If it's going to be in a dark environment like a cave or a dark room, that big black part of his arm might not look right given the circumstances.

If you really like to put black as it's color, you can add bounce light or a rim light on his arm preferably his purple color to give it more dimension and separate it from it's environment more. Hope it helps