Before I click the thumbnail, I really like the white balance / color balance. It looks perfect (see the right thumbnail). When I then double click the thumbnail to open it, Rawtherapee automatically applies some processing changes. The resulting image (and thumbnail) changes, and the colors look way worse imo.
How can I just use the processing profile that is used on the thumbnail, before I click it?
I think, what you see first is the embedded JPEG-preview generated by your camera. So basically the same what you get, when you shot JPEG. The raw is only minimally processed when you open it in RT.
the docs are quite helpful here: Editor - RawPedia
I am not a RT user, but in darktable I set my white balance to as shot in camera. I presume RT has a similar option and this may resolve your problem.
Here is a detailed elaboration of Thomas’s answer: http://rawpedia.rawtherapee.com/Editor#Eek.21_My_Raw_Photo_Looks_Different_than_the_Camera_JPEG
IMHO, if you love color or white balance of OOC Jpeg of Canon cameras, you should use DPP4. With any third party raw processor, you cannot fully emulate OOC Jpeg, even with commercial raw processor.
What is DPP4?
Canon’s own software. Only Canon knows exactly how they produce the in-camera JPG.
But if you like your in-camera JPG, why not just shoot in JPG, and make smaller adjustments to the JPG files, when needed?
You can download DPP4 from following link for free.
With DPP4, you can edit your CR3 files, or export to TIFF files and edit them with RawTherapee.
In RT, using dcp file of your camera model, you may get similar result with OOC Jpeg, but not identical. If RT does not contain the dcp file of your camera, you can get it from Adobe DNG Converter for free.
