Get some Luminous Color Glaze by John Frieda! They sell it at the drugstore, for less than $10. It lasts a long time, too. You can use it as a 30 minute or so treatment, or do it everytime you wash your hair, just as you would a conditioner. I use the clear on my hair. It will pick up your highlights a bit, too.
Don't start glazing as soon as you color or have your hair done at the salon-- enjoy what you spent your money for. But when the glow starts to come off... You can buy the JF in the same color as your hair, but I get my hair colored and highlighted so I only use the clear.
Also, I guess everyone knows to wait a few days to wash their hair after they color it, use a shampoo for color treated hair, and don't wash your hair so much. You can just rinse with water without having to shampoo up , and it helps keep the color fresh.
In my quest to avoid constant hair washing, I have also become a big fan of the All Nighter. It is a styling powder you use when your hair starts looking oily. It comes in shades to match your hair,and it is great stuff. You just fluff in a little and poof- fresh hair that smells great. Stylists use it a lot. You can experiment with it to see how much you need and how much you should work with your hair (usually not much) after you have applied it.
I have lots of very thick, coarse hair, and it works for me.