@mummydactyl typically I redye once every 4-6 weeks. This picture is kind of deceiving, it doesn't show the bits that are rather candy floss looking and the roots at the back of my head are completely yellow (thanks to sweating like crazy in the nasty above average temps). The hair at the back of my head fades a lot quicker than the front bits which seem to hold onto color forever.
Snapped this pic right before I dyed over it LOL.
I think everyone's hair is drier at the front. Even my 5 year old has dry hair at the front, which makes it extra tangly! I have yet to find some kind of treatment that evens this out... Thankfully keeping my own hair so short it doesn't matter so much for me at the moment, though both my girls could do with a little help!