Scroll down to Resin Tinting in this post. I had very good results pigmenting Clear resin using the nano-dispersion I linked near the top of the page. Others have reported success using dyes intended for epoxy (search the forums).
High Temp already has an orange tint and I imagine you could darken it substantially. I’m not sure you’ll be able to get all the way to black before the opacity falls too far outside the laser profile, but if you try it let us know how it goes!