For Juno you need to look for Atom skins and Syntax Themes (found in the atom package repository). The color scheme of your terminal (not syntax highlighting) can be changed in a million ways but that is platform dependent and even application dependent.
If you instead are referring to the syntax highlighting in the terminal REPL, that is handled by the Package OhMyREPL, you should look into the documentation as there are ways to change the color scheme.
For both points in your question, either you find a theme that suits you or you modify the one you are using. In both cases you will find much more accurate informations in the respective forums/guides.