As a kid I loved to colour, and have fond memories of going to my Grans house with the worlds largest collection of colouring books. Her collection spanned all the way back to when my own mother was a girl!
As my nieces and nephews have got older and started to enjoy colouring, I have started my own collection, however mine is a slightly more electronic version. See, I scan all the pictures before they are coloured, so that we don't have arguments if two little people want the same picture.
But, I have since discovered these silicon colouring mats that can be wiped clean after use and reused! Genius!!!