This is no problem when you are creating a rug with many colors in a mixed pattern, but if you want a rug with distinct bands or rows of colors, you will develop what we ruggers call the "Stair Step".
It can be visually distracting for those who want a more even transition with a change of color.
|How to lose the stair step in a knotted rug|
Each time you want to change colors, You END THE RUG, and then add a new strip/color as above. If you want two different colors, one for the working strip and one for the runner, add the new runner color at the end of your "tail".
To see how I end my rugs, visit this blog post:
End a Rug
Here are some rugs where I have used this technique:
|No Stair Step look on these Toothbrush Rugs fourelevenrox - Whitehouse Whimsies and Rugs|
It works on oval rugs too! The trick is to change colors in a different spot each time. This will avoid to much bulk, in the same area of each rug and make the transitions smoother.