Overlocker; choosing yarn colors

Hi all,

I'm about to purchase my first overlocker -probably the Juki MO 654 DE, for the curious among you- and i can't find the answer to one question i have:

How do you choose yarn colors. I've heard it say that some use those 4 colors, like the threading guides indicate. And others use only white, i think? Does it have to do with the loopers and needles and what is visible on your fabric?

So, those of you with an overlocker; what do you do? Is it like choosing yarn colors with a regular sewing machine?

And bonus question; do these yarn cones last as long as they would on a sewing machine, or do overlockers consume more yarn per cone?