
I think most breeders of boxers would now register them or at the very least raise them the same as any other colour, however there are very few if any owners of white boxers in the UK that breed from their dogsto another white boxer(unlike "white" GSD owners were there are many breeders who breed "white" to "white")
I knew one of the top Boxers breeders from the middle part of the last century & she originally used to cull any whites born in the 40's & 50's, then in 60's stopped culling but did not register them & towards the end of her life used to register them & put restrictions on them(she died in the 70's)
With pets colour is simply a personal choice, but for the show ring the breed standard is the template of the ideal dog that breeders should thrive towards breeding