Ink cartridges. Do they go bad? Available wholesale?

Howdy, Folks.

Welp, I can't figger it out (yet). My printer is printing just fine but I'm not getting true color. My HP Toolbox shows I have 50% black ink left, 30% color ink. I can't see replacing a color cartridge that has that much ink left.

Is there a chance that it has gone bad? Do they dry up inside or something? I believe I replaced that color cartridge in the not too distant past, perhaps 6 months ago.

I've gone thru the tools, cleaning, running print tests, etc. Still no go. Any suggestions on what to do next?

As for the "wholesale" in the subject line above...does anybody buy them by the case at a reduced rate and if so, where? And if you do, are their expiration dates on them so you must use them up fairly quickly? If not buying them wholesale, is there a less expensive source for ink cartridges (other than the refill kits)?

Thanks for any input!
Shoe
(PS I am referring to inkjet, not laser, just in case there is a difference between the two types of printers.)