Random Color Questions

Is it possible to change the cyan text color on the menu? And is it possible to change a color in a palette?

I know you can change palettes for objects, but don't know if the palette itself is changeable. Specifically I want to change the dark purple or whatever color is in dungeons that is supposed to be black. I'm sure it's not pure black because that is supposed to be damaging to televisions or something like that, but the purple almost shines on my LCD, it's very distracting, so I wanted to substitute black (or even dark grey).