On the next row you'll do the same thing, working stitches in yellow on the gray side (in this example) and gray on the yellow side to make the color pattern appear.
Again because this is practice, don't worry if you mess up and work a stitch in the wrong color. Just keep working in this manner for as many rows as you like.
For symmetry you will probably want to work a few rows in a single color on each side just like you did at the beginning. To change back to solid-color knitting from your pattern, start working all the stitches on each "side" in a single color instead of working some in each color.