I’ve posted recently (here and here) about libinklevel and mentioned the simple command-line client, simply called “ink“.

For the graphically-inclined, there’s a pretty nice GNOME app called “inkblot” that an put a status icon in your tray and you can click it to get more detailed information.

My printer has 6 ink cartridges, but inkblot only shows levels for the cyan, magenta, and yellow. Presumably it is rolling cyan/photo cyan and magenta/light magenta into one number and it seems to be doing this by taking the lesser number in each pair.