I have a Lexmark color printer, for a computer. 

And, I just purchased extra ink cartridges for future use.

What is the best way to store color (and black) computer ink
cartridges, so they do not dry out?

Hi Clicker!

Very good question.  If you're like me, you'll be sure to have extra
black and color cartridges accessible for 'just in case' one suddenly
empties.

The information provided below applies for all cartridges used in
computer printers.

From the website e-cartridges.com  (This url is from a cached version
of
the e-cartriges.com site)
http://216.239.39.100/search?q=cache:7aY0BiMWdvEC:www.ecoqualitysys.com/faq/middle.html+Storing++printer+cartridges&hl=en&ie=UTF-8

"Storing and handling toner cartridges     
Store toner cartridges in a cool dry area, always in the original box
with the arrows pointing up. Never stand on end because the toner may
leak when you put the cartridge in the printer.

If there is a big difference in temperature or humidity between the
storage area and your office leave the cartridge near the printer for
a couple of hours.
    
When installing a cartridge, slowly rock it 45 degrees about its long
axis about five times to distribute the toner evenly.

The drum in the toner cartridge has a photo sensitive organic coating
that deteriorates when exposed to high temperature or strong light.
The toner in the cartridge can also be affected by high temperature
(toner melts at 40 degrees Celsius). For this reasons do not place a
cartridge in direct light or near a window."


Same advice different website
Using and Caring for Your Print Cartridges: HP DeskJet 950C Series
Printer User's Guide
http://support.ap.dell.com/docs/acc/hp950c/cartridg.htm#storing

"Storing Print Cartridges
To maintain excellent print quality from your print cartridges: 

1. Keep all print cartridges in their sealed packages, at room
temperature (60-78° F or 15.6-26.6° C), until you are ready to use
them.

2. Once installed, leave the print cartridges in their cradle at all
times to keep them from drying out or becoming clogged.

3. Store unsealed print cartridges in an airtight plastic container."

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I like to keep mine stored in a desk drawer (away from sunlight)
inside a large sealed plastic freezer bag.  Or you could use a
filebox.  Anything that will keep them protected will do nicely.
  
Search terms:  "storing printer cartidges"  "printer cartridges"

I hope this information is helpful!

tlspiegel-ga

Thank you tlspiegel:
I rate the answer with 5 stars.  
clicker5

Thank you clicker for the nice rating...

tlspiegel

Some of the above answer related to powered toner cartridges.
For Ink Jet cartridges, sometimes the jet nozzles will dry out - even
sitting in the printer.  If you have a Lexmark ink jet printer that
has only one spot for a cartridge (ex. Z-11) and you have several open
cartridges, you can place the spare cartridges upright in a sealed
zip-lock bag, with a cotton ball wet with rubbing alcohol. I have used
this method and it has allowed me to keep cartridges in good shape for
a year or more.