>>>>>> I just checked again, and list-colors-display only lists eight 
>>>>>> colors in a raw Linux console.
>>>>> 
>>>>> What does display-color-cells return in that case?
>>>> 
>>>> 16777216
>>> 
>>> Then I guess linux.el should call the same color setup code as 
>>> xterm.el does in this case.
>> 
>> That's the value I get on my system, is it guaranteed to be the same on 
>> other systems?
>
> Answering my own question: no.  I just tried on another computer, with a 
> similar kernel (5.17 instead of 5.18), and there display-color-cells 
> returns 8.  So I guess we use the most conservative value here.  We 
> could make the (xterm-register-default-colors xterm-standard-colors) 
> call conditional to the return value of display-color-cells, though.
>

Answering my own suggestion: no.  I just tried, and for some reason it 
doesn't work.  Here's a screenshot of list-colors-display with 
(xterm-register-default-colors xterm-standard-colors) in 
lisp/term/linux.el.  As you can see, bright colors and non-bright colors 
are displayed in the same way, and other colors are displayed wrongly. 
Perhaps there's another way, though.