For each serving, add 2 Tbsp of that color. So you'd have 2 Tbsp Red, a heaping 1/3 cup of orange, 1/4 cup yellow, 1/4 cup green and 2 Tbsp blue. We give examples of foods for each color in the book!
In most cases the color of the fruit or veggie is the "color" that we are talking about. However, there are some wildcards. The book, Nature's Prescription for Optimum Health, that comes with the NutriBullet Rx helps explain this in detail.
If using the website, then search for recipes and foods that correspond with the color's theme.
Example if you got more red then search for anti-aging. Yellow would be anti-inflammatory, orange is immune boosting, and blue or purple is brain-boosting, and green is detoxifying.
Hope that helps!