A few drops of a dye such as https://www.amazon.com/gp/product/B06XD39K55/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
works like a charm on any 2 part epoxy that I've tried it with. Never had any issue burning or weakening epoxy when using a MAPP torch and keeping it moving.