Sure, you could spend your whole life happily knitting away in one color. Or you could cut loose and explore the full range of wild and wonderful colorwork techniques. Even just two colors will give you a whole slew of techniques to try, from beginner-friendly stripes to more complicated double knitting.
Easy Colorwork Techniques
While not generally thought of as a colorwork technique, marling deserves a moment in the spotlight. By simply holding two or more strands of different colored yarns together as you knit, you create a fabric that has an interesting allover color pattern.
Stripes are one of the simplest two-color knitting patterns. Once you get the hang of changing yarn colors, you're good to go! Your stripes can be thick, thin and everything in between.
Sometimes called picture knitting, intarsia is worked by using separate balls of yarn to make blocks of color. The colors are not carried across the back of the work (as with stranded colorwork), making it a great beginner option (though, not all intarsia is created equal: this technique can get quite advanced, too!).
Intermediate Colorwork Techniques
Stranded colorwork involves carrying (or floating) two or more colors along the back of the work. Start with two colors and, if you're ambitious, work your way up to four.
Mosaic knitting, a variety of slip-stitch knitting, creates cool geometric patterns with a very simple premise: you only ever work with one color in each row. By slipping stitches from the previous rows, you get a two-color effect that is deceptively simple.
Advanced Colorwork Techniques
Brioche knitting is a beautiful technique that uses one or two colors to produce a reversible knitted fabric. There's no wrong side; the colors take turns being dominant in the pattern to produce a unique look.
Like brioche, double knitting creates a reversible knitted fabric. It's like creating two layers of knitted fabric at once.