The site doesn't explain--what's the actual point of this? If we are seriously concerned about characters (which is generally silly in a gzipped CSS) why not just use 3-char hex like #a5c?
No, TFA does very deliberately and openly explain what the goal/justification is:
> Splash colours can help you avoid decision paralysis when picking colours. It's an emotional tool that stops you fussing around— trying to pick the "perfect" colour … It also means the user can deal with discrete / individual colour values in the drag-and-drop user interface. They don't have to deal with large numbers at all. Only one to nine
Avoiding analysis paralysis, making it more intuitive to manually write colors. But yeah, there doesn't seem to be any advantage over the well-established #ABC format than decimal digits being easier to non-techies.