The Machinery supports industry standard methods for color grading for HDR colors. Currently, there is no support for custom tone mappers:
The Color Grading component allows you to use either Lift/Gamma/Gain controls or ASC-CDL controls. Regardless of the method used, the shader will apply a single ASC-CDL transform per channel. The resulting transform is visualized using the graph. Color grading is applied just before the tone mapper in ACEScg space.
The Color Scopes Tab can be used to visualize the color spread in your scene. This might aid in color grading.