A long, long, long standing annoyance of mine has been these details of the original Base16 style guide:

base03 - Comments, Invisibles, Line Highlighting

I don't think comments should be relegated to the same level of "visually unobtrusive" as whitespace markers. In fact, comments can be considered more important to see than eg. keywords, because the compiler can't see them, the human has to.

At a minimum, base04 or base05 should probably be used for comments.

In a similar, but less official, vein: in several of the terminal and TUI templates, the eighth colour (counting from 0) is often base02. This is more debateable, but note:

• base01 is typically the background (not base00), so it's only one increment up from the background
• there are only 8 official ANSI colours
• colours above that are either modified ANSI colours (bold, high intensity, underline), OR
• actually taken from the xterm-256-color set

In general, I think it'd be far more sensible to use base03 or base04 for this eighth colour in terminal templates.

That's for the original Base16 guidelines, but I've noticed a similar trend in Base17 and Base24 as well, so consider this my plea to consider this carefully while this project is starting out. Otherwise you'll end up in the same weird feedback loop where scheme designers deliberately skew base02 to base05 to have greater contrast (or even colour) while template designers use higher baseNN numbers for greater contrast based on the original theme or style guide.