Color support is important, but 256 has served me well for decades. Can't think of a single program that would benefit from more colors. Unless, of course, you're trying to watch ASCII-videos.
- Themes, its nice to have the same color scheme across your programs. You can always redefine your 16 base colors in the terminal and map these to syntax in your terminal program (e.g. vi), but it's cleaner to have the rgb colors directly in your theme file, especially if you switch themes (I don't do it too often, but I like to change colors every month or so to keep it looking fresh)
- If you code CSS, it would be nice to have preview of #336699 colors in your editor. To implement that, you need real color support.
- And, less important, for those who play nethack-style games it's probably nice.
Because my fave 256 aren't the same as yours, and palette switching is a huge pain. see for example what a pain it is to get Solarized working across both terminal and X and ssh sessions, in vim and emacs.
Kind of a side rant but I've often wondered why Apple doesn't put more effort into making Terminal.app better. Macs are rather popular amongst certain types of developers and making their life easier is a nice way to make sure they'll keep on using Macs.
Read ECMA-48¹, which is the free (as in beer) printing of the ‘ANSI’ terminal controls standard. If you want to supply text (like a file name), you'd probably use an OSC command ESC ] Ps ; Pt ST with a Ps that no one else is using. To mark the start and end of a region, you'd probably use a pair of control sequences (CSI) analogous to START / END OF SELECTED AREA, from a private use range.
(The true-color sequence comes from an ITU recommended extension / future version, T.416². It would be interesting for the OP site to list which terminals support the full proposal, including CMY an CMYK specifications, as well as RGB.)
Some terminals already detect URLs by pattern and make them clickable. You could also add an escape sequence to create the annotation you describe, then modify a terminal app to support the sequence. However, terminals don't always display trusted data, so it's very risky to add escape sequences that do anything more than display formatted text.
For example, there are sequences defined to change the title of the terminal window or print to a printer, but they are frequently disabled or left unsupported for security reasons.
Wait, we're settling for 24-bit color? With HDMI and modern image and video formats supporting 10-bit and 16-bit channels, I need a terminal that can support Deep Color.
True HD color with 64-bit depth, including a 16-bit alpha channel, is the minimum future programmers will demand to syntax highlight our source code and identify monsters in Nethack.
Sarcasm? I find it sometimes hard to tell around here.
But seriously, I like the meta-idea of putting up a site to promote a technology; with a list of compliant apps for users, and information how to implement it for the developers. I'm thinking about making a site that catalogues DPI aware software for windows (like Macs "Retina"), because its annoying how many programs don't support high DPI screens properly, and its notoriously hard to do for developers.
Color support is important, but 256 has served me well for decades. Can't think of a single program that would benefit from more colors. Unless, of course, you're trying to watch ASCII-videos.