I wonder if there are really tiny fonts that make use of color. For example, this 2-pixel wide Picket Right font could theoretically be even thinner if we were to use sub-pixel features.

At least, I think the 2-pixel high Two Slice font can be more legible with some anti-aliasing.

Yes. https://advent.blinry.org/2018/17

Don’t stop at colors. Just add a ligature for every string and support for animations and you have yourself a font that can render any alphanumeric string in a single pixel. I’ll need to brush up on Morse code though.