The first thing you need to do is choose a shampoo and conditioner designed for color-treated hair. These will help protect your hair from the elements. Once you have to right products, dont over use them. It is alright to go a day or two without washing your hair, as over shampoo can strip your hair of the color completely. On days off, opt for a dry shampoo instead.
Additionally, you should deep condition your hair at least once a week. This will not only help keep your color looking richer longer, it will also protect your hair from any damaged caused by coloring. But dont just stop with shampoo and conditioner, add a little sun protection. The UV rays of the sun can be damaging to your hair, so be sure to spray on a styling product that also has SPF.