had the same thought since it couldnt be for herself just to go out undercover because she could just wear another colour and doesnt need others to wear it but rather someone who should have blue hair doesnt have it or at least maybe not the right blue? ( RATHER SAD SINCE YOU CANT CHOOSE YOUR HAIR OR EYE COLOUR EVEN WITH SRTONG TRAIT NOT EVERYONE GET THEM) but then again if she said its to make sure a child can have the colour i think it would be alright to make the wig only once or even take it of once more people get used to having different hair colours so they could say later the child really likes that hair colour :D and maybe someday they care less
I think its a child that doesn't have that blue hair and so won't be recognized as part of the royal family. Purely my guess tho