Feature Request: Custom primary color

[wurst-hans]

I'm running your watch face on three watches now. I'm using the THEME_BLUE_DARK but I loooove the blue color of THEME_BLUE_LIGHT which is different from the dark mode (even the blue color on the image in app store is different from the blue dark theme)

So, I suggest to let users choose a color completely customizable by adding an option to type in a RGB value and a switch for turning light mode on and off.