I use color printing very sparingly, I wonder if it is good to put back on the plastic sticker that came with the printer cartridge when you want to prolong cartridge life (or to store them) ?
As noted by @DragonLord, the printer caps the cartridge when installed and properly shut down. Properly shut down means that the printer is turned off using the power button and not switched off with a power bar or similar. Using the power button assures the capping mechanism moves into place and covers the print head properly.
Cartridges have a small air hole that allows ink to flow when in place. This means that there is air above the ink and the ink slowly dries over a period of time. In many cases, it is not the fact that the ink dries out but that small flakes/bits of dried ink fall into the cartridge and clogs the print head or another part. That is hard to avoid if the printer sits for long periods.
Removing the cartridge allows air into the print mechanism (possibly a print head) and if that dries, the cartridge will fail to deliver ink due to the dried ink in the mechanism.
One of the best things you can do is print a test page or something every so often as that keeps ink fresher in the print mechanism and you also need assure proper shutdown of the printer.
If the cartridge is installed in the printer, this is not necessary, as the printer will automatically cap the cartridge so that it does not dry out. If this cap is not effective, you may need to remove the cartridge and try to seal it.
If the cartridge is not installed, yes. Ink can dry out if the cartridge is exposed to air. For this reason, new ink cartridges are generally packaged in a sealed wrapper inside the box.