Color cycling and some way to limit the color picker to emulate certain graphics chips and console limitations could be cool, like the CPS1's 16 bits with RGB and a "brightness" channel, the amstrad CPC's 3 level-per-channel, or Amiga and Megadrive's capability for Extra-Half Brite mode, along with the more straightforward "X bits per channel" setting
I was thinking less of the color palette in the modern sense and more as in the actual whole available array of colors available to a console or PCB. Like, there'd still be a way to make palettes, but the colors you can pick to make said palette would be limited, if one chooses to do so. "Color Gamut" could work as a term. And for consoles that have features like EHB or NES' "color filters", there should IMO be a way to toggle them so as to make accurate color picking easy (easier?), maybe some sort of "brush" to change colors to their equivalent in the EHB or color-filtered gamut? Glad to hear indexed mode is being worked on, though!