I'm always tempted to buy colored mascaras when I see them but as we all know mascaras have a pretty short life when opened so I hate to spend money on fun mascaras!

What I do if I want to color my lashes is use a liquid eye liner or even glitterliner, to paint the tips of the lashes after using a regular brown or black mascara. Now, it'll obviously clump pretty bad if you apply it all the way from root to tip of the lash but it actually looks pretty good if you only paint the tip (or a little more) of the lash! :)

I know that MAC has an eyelash mixing medium (and other brands probably do as well) but I've never tried it so I can't tell you how that works.

Here's an example using MAC Greenplay lll to paint the tips (well, a bit more than the tips, actually) of my lashes:

Sadly, my lashes are neither very long nor full to begin with but I still think the pop of color is a nice effect :)