Hi @johannes - Color.io doesn't support LUT loading right now because most LUTs are not color managed. Color.io is color managed via ACES and works in AP1 gamut internally. A LUT would have to match that color space and gamma to work as you'd probably expect it to. Color.io is really designed to be a tool that creates really good, fully color managed lookup tables. Loading external LUTs into this pipeline would very likely throw off the rendering integrity.

If you need external LUT support in addition to the tools in Color.io, please open a Feature Request, so that other users can chime in and vote for your idea. This helps me decide what to focus on next with development!

For now, you can manually match existing LUTs by hand. I recorded a video for another user a while ago that shows the process of manually matching an ungraded image, to the same image with a look (or LUT) applied: https://vimeo.com/846588637?share=copy#t=75