It's rgb with 3.3 bits per channel, basically 10 bit per pixel color (256 colors is 8bpp).

The point is that quantizing the range makes it easier for humans to choose colors. But there's already the #ABC hex format, which while less intuitive to non-techies has the huge advantage of being well-established.

My other question here is, are "R", "G", and "B" channels the best way to reason about color? Isn't HSV more intuitive?