Nice game ! I‘ve been trying to implement mobile controls to Pico 8 but I haven’t really found a way out, unless using someone else’s code. How have you done your mobile controls ?
I used this PICO8 HTML Template. Without knowing any javascript, you can choose from a number of buttonsets (even a joystick if you put special code in Pico-8) and you can change the colors of those buttons. If you're looking to build your own from scratch though, can't help you there, but it may be helpful to look over the code for that template.