Likewise for the Televideo 995-65: http://bitsavers.org/pdf/televideo/995/firmware/

This is not, as the function name suggests, a colon, but per ITU/IEC T.416 it should be:

https://github.com/cosmos72/twin/blob/truecolor/server/hw/hw...

And not only should this have colons too, but per ITU/IEC T.416 there's a colour space parameter that goes in there:

https://github.com/cosmos72/twin/blob/truecolor/server/hw/hw...

The unfortunate part is that when rendering to a terminal, you don't have any available mechanism apart from hand-decoding the family part of the TERM environment variable, and knowing who made which mistakes, to determine which of the 7 possible colour mechanisms are supported. They are:

1. ECMA-48 standard 8 colour, SGRs 30 to 37, 39, 40 to 47, and 49

2. AIXTerm 16 colour, ECMA-48 plus SGRs 90 to 97 and 100 to 107

3. XTerm 256 colour, ITU T.416 done wrongly with SGR 38;5;n and SGR 48;5;n

4. XTerm 256 colour corrected, ITU T.416 done right with SGR 38:5:n and SGR 48:5:n

5. 24-bit colour take 1, ITU T.416 done wrongly with SGR 38;2;r;g;b and SGR 48;2;r;g;b

6. 24-bit colour take 2, ITU T.416 done wrongly with SGR 38:2:r:g:b and SGR 48:2:r:g:b

7. 24-bit colour take 3, ITU T.416 done right with SGR 38:2::r:g:b::: and SGR 48:2::r:g:b:::

Few people support 4, and although quite a lot of us have finally got to supporting 7 it isn't quite universal. Egmont Koblinger, I, and others have been spreading the word where we can over the last few years.

This is where I was at in 2019:

https://github.com/jdebp/nosh/blob/trunk/source/TerminalCapa...

There a few updates to that that are going to come out in 1.41, but when it comes to colour they're mainly things like recognizing the "ms-terminal" and "netbsd6" terminal types in the right places.