Freezemarking White Hair?

[domane]

I want to have my yearling hairy coblet freeze-marked and I know they have to keep the markers on for longer to kill the hair follicles completely. Unfortunately he's white everywhere where he could be marked so I don't have another option. I just wondered how reliable this method was as I've heard of a few cases where the hair continued to grow and the letters were only half-formed or disappeared altogether. How many of you have successfully had white or grey horses marked, please?

 

[the watcher]

Yes I have had a grey marked very successfully, in fact because she was black skinned her freezemark really stood out

 

[Dubsie]

The Sec A my duaghetr used to ride is a very white grey. In the winter her coat almost completely covers it, but you can see it if you were grooming her.
In the summer, her shorter coat doesn't cover it as much and you can very clearly see all the letters