You can already plot multiple functions actually, by listing them with commas, like so :)
f(x): x^2
g(x): sin(x)
f,g
Naut will "print" whatever it sees on the last line. If you give it a function (or a list), it will plot it (or them), and if you give it multiple numbers, it will print them.
It's a good idea to hover and highlight though! Custom colors could also be a thing, just need to add the idea of saving them to a user file somewhere (right now Naut doesn't load/save any data, it's self contained, but it wouldn't be a problem for "user customization" to live in some other folder I think)