I recently dyed my medium blonde hair using Revlon Colorsilk to the "Light Auburn" shade.
I've been told by many people that red is the hardest hair color to maintain (using hair dye).
I did some research and came up with these options:
*Soak hair in v8 vegetable juice for 20 minutes (got that one from Allure magazine)
*Using a henna based shampoo/hair rinse
This is the red I'm going for: