I'd like to expand on this idea a bit. It'd be great to be able to specify a cell as being either an RGB channel or a single-color channel specified by a color picker.

And to make custom models a lot easier to create, it'd be nice to be able to paste in an image into the spreadsheet, have a button to dim it or turn it off, and then you could just go through and type numbers to match the "template" image. Maybe you could even toggle between seeing the model represented by numbers or their corresponding colors.