How can I stop wasting my leftover colored inks

If your printer has separates ink chambers than it is possible to remove empty one and replace it by new one.

http://www.inkjetkarts.com/canon-printer-ink-cartridges.html

What sort of Epson printer do you have Jad?
I had a similar frustration with my earlier model.

I think what Steve's getting at is that if you print photos with less of the color you are using the most of, then all the ink colors should finish more evenly.

There is still the question of what to do with the ink you have leftover, which is the wastage issue. Not sure, unless you put them aside and can seal them up to use them later if you find you are low on them at some stage.

The problem with older inkjets as you've found out, is that you use one color too much then have to throw out the whole thing. The new printers separate the ink colors individually so that you can just replace the one that is being used.

If you have a 3 ink system and you are constantly using more of one...I'm guessing its possibly the Cyan???
I generally use more blue(cyan) than any other color.

The only way to get by the problem would be to print photos that contain less of the color you are using most. If you were running out of cyan first.. it might be because you were printing a stack of outside photos with sky backdrops. Peoples clothes tend to often contain blue as well.

That's of course the simple explanation. It could be a problem with your ink feeds on the other colors though ie. more of one color is getting fed than the others.

Don't know if that all makes sense..

Steve