Do some colours fade faster than others?
This is somewhat true. That is why it is important for you to choose a reputable and qualified artist ensuring that proper technique has been used in the application of your tattoo. Following proper after-care and maintenance procedures are also crucial in ensuring the longevity of your tattoo.
The main cause of a properly applied tattoo fading would be the sun. The better you take care of it, the longer it will stay bright, vibrant and crisp looking. If you are a sun worshipper...pull out that sun block. All tattoos will however fade somwhat after time no matter who did it or how good the ink used is.