pretty sure its a no on the hair dye ,tried it a couple of times ,washed right off no color change ,
i now use a permanent marker ,its a bit fiddly ,but with a bit of care and preparation it works like a charm ,
a limitation is you can only go darker but sounds like thats what your after
heres what i do ,first mask of the face ears etc ,with tape or cling film
then put down paper on a flat firm surface ,tilt the head on its side and spread out the hair ,
then starting at the parting draw the pen through the hair ,top to bottom ,
this streaks the hair with color ,its up to you how many times you draw the pen through ,to get the result you desire
advantage is you can add more at the parting and streak it through and it will have a natural multi tonal effect like real hair does
ie darker at roots equals new growth verses sun lightened at the tips ,
let it dry and do the other side ,and then the back ,once dry its safe to touch with no color transfer
if you want to style it after and intent to use hair gel ,be advised to leave the tape on at this stage ,as most gels have alcohol added as a drying agent and can cause the color to run ,doesn't hurt as it helps even the color out overal
for darkening blonde hair id go for a light brown and just lightly streak it through ,its surprising how little can darken so fast , but please make sure they are permanent ink markers your using
id recommend you try it out on thrift store ,charity shop barbies first to get the feel of the technique , and then move on to your main one
good luck and post your results
heres a mera i made ,green suit is how the hair was ,blue suit is colored in with a pen
View attachment 430668
:goodluck
barbie mera suit boots and gauntlets, on a new body with a head i got from ebay ,hair recoloured with a red permanent marker , which actually works out ok much to my suprise :lol