When I tell people to eat a rainbow of colors I do not mean rainbow skittles. This means that people should be eating a variety of colorful fruits and vegetables every day. In fact, the recommended serving of fruits and vegetables is 9-10 servings!
One way to ensure you are getting a variety of colors is to make the produce section your first stop in the grocery. Before you leave this section, check your cart. Try to aim to have a fruit or vegetable from each color category. This includes blue/purple, white, green, red, orange, and yellow.
Planning ahead can ensure you are shopping for enough fruits and vegetables. Make sure every meal, especially lunch and dinner, contain a non-starchy vegetable. Get outside of your comfort zone and try fruits and vegetables that you are unfamiliar with. Another suggestion is to make it fun by finding recipes that include more than one colorful fruit and vegetable and also help bring out the flavor of that vegetable. Remember vegetables don't have to be plain and boring.
Keep in mind that frozen vegetables are also a great choice. I always aim to eat my fresh vegetables first so that I eat them while they are ripe and before they go bad. Towards the end of the week I rely more on frozen fruits and vegetables.