@jenny-lou you can switch colors in normals the same way you would in alphas. The technique could be applied to any pattern, and video tutorial can be found on #43509 called Changing Colors by @Racoon.
Another option would be to use variegated red and green thread, tho you wouldn't have much control exactly where the color change would happen. Just make sure to line up all 3 threads at the same color-changing point to get a more uniform look throughout the pattern.
