Always interested in trying out something new -- especially from independent developers & enthusiasts. But... (from RawPedia on the Color Preferences):
"On Mac OS X all displayed colors will be in sRGB space, and then, if necessary, converted by the native OS X color pipeline to match the screen calibration, if any. This means that you cannot choose a monitor color profile on OS X. Colors will be displayed correctly, even over multiple screens, but if you have a wide-gamut screen RawTherapee's displayed colors will still be limited to sRGB. This will however not affect output, i.e. you can still produce images with colors outside the sRGB space."
What a pity. At that point, all the elaborate de-mosaicing, exposure, tone and color management tools become (mostly) useless.