One potential problem with knitting with multicolored yarns is color pooling, that is, a blotchiness of colors in the knit fabric that's usually considered unattractive.
Color pooling is relatively unpredictable. You can knit a swatch in the pattern stitch with the yarn you want to use, but because you'll likely use more stitches in your project than you did in your swatch, a lack of pooling in the swatch doesn't always mean you're home free.
Watch the color development in the first couple of inches of your knitting so if you're seeing a trend you don't like you can try to correct it before you've knit the whole project. Here are a few things you can try.
Change Your Gauge
The first thing to try when you see color pooling in your knitting is changing your gauge if you can. Projects that don't have to be an exact size can often be worked successfully on larger or smaller needles, and the little difference can be enough to break up a color pool.
Change Your Stitch Pattern
Different stitch patterns take up different amounts of yarn, so you can get a different color distributions just by switching from, say, Stockinette Stitch to Garter Stitch.
Throwing in a few slip stitches can break up a block of color, too, since slipping a stitch makes the color from the previous row visible.
Whichever method you try, you'll still want to knit a swatch to ensure that you like the look you're getting from the new stitch pattern as well.
Add a Stripe
As you may have noticed, the key to breaking up a color pool is to get different parts of the yarn near each other. Another way to do that is by working a stripe every couple of inches to separate the offending colors.
If you don't want to add another color to your project, work from two balls of yarn at once (or from both the center and the outside tails of the same ball). Knit two rows with one ball, then two rows with another. It's unlikely the colors will line up the same in two different balls, so that will break up the color problem.
Call it a Design Feature
Some people like pooling in their knit projects, or at least are willing to accept it. If you're knitting with a hand-dyed yarn in particular, it can be nice to just leave the project as it is, letting the organic nature of the whole process of the yarn's production continue into the knitting.
Even if you're not using hand-dyed, you can still consider color pooling a design feature and decide to do nothing at all about it. It's your knitting project, do what you like.