Best and secure way is to take your watch to a watchmaker >
get the watch disassembled, then if he has been around for sometimes he will know what to do to tint the tritium to get it close to perfection for your liking.
Other methods include heat and light, heat for the inside of the watch case and light 'UV' or power light fixing the dial. Then you get some reaction, only at times it ends up too much or too long to get a result.
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