apt-cache search color picker
which returned 3 results, including gcolor2.
First off, this is exactly the application I needed. It launches fast, and just gives me a color wheel to pick colors. But, it turns out it has something else that’s great.
You see that little eye dropper? You can click it and then click any pixel on your computer, and it will give you the RGB color of that pixel. It doesn’t need to be anything special, as it’s pulling directly from the xbuffer. So handy. I can’t believe I didn’t know this existed until now.