Treated colored diamonds

I in search of as to how colored diamonds are
treated to change their color. I understand that they are
irradiated, but what type of beam electron or neutron I am not
sure. Are the diamonds then heat treated afterwards? How deep
into the stones does the color change go? How does heat change
color? Is the color permanent? Any help or leads will be greatly
appreciated. many thanks

etienne perret
@etienne_perret