As I'm currently a red head, I'm battling the war of remaining red. Red dye apparently has the largest sized molecules, which makes it hard for them to penetrate the hair shaft. Ironically, red stains the shaft and is very hard to remove, but to keep it vibrant, you need to commit to the work it takes!
Currently I am redoing the red dye almost every wash. I stretch it to every other wash, but only because I get lazy. Luckily I only wash it once a week!
When people come to the salon to go bright red, I always advise how much work it takes to keep in looking awesome. I have played around with different colour products, dyes and techniques, and finally found what keeps it brightest, but it is still a very regular process!
How much effort do you put into your hair colour?