Please link to the pattern if you can so we can see it. It helps us help you.
What does the pattern say? Generally with large blocks of color you use the intarsia method. It's done flat. You can find a video at the tab at the top of the forum in advanced techniques.
In some cases you can carry the color across using fair isle (also at the tab above). If you have multiple colors on each row this isn't recommended because you'll just have too many strands across the back and it'll be very bulky and awkward to do. It's usually done in the round.
When asking questions ALWAYS post the name and a link for the pattern if you have it.