My Ds is way too young for colouring books but I'd dragged him into town to buy a present for my cousin who's 5. As I was looking I saw this little girl pick up a spiderman colouring book and ask her mum if she could have it. Her mum said spiderman is for boys you can have a princess one. The girl didn't want the princess colouring book as the spiderman one was better.
The poor girl didn't get a colouring book in the end as she wouldn't accept the princess one 
AIBU to think that it doesn't matter what type of colouring book a child wants as long as they are happy? If Ds wanted a princess one he'd get one, same as if he wanted a spiderman one