Mari 4.6v4 docs:

View Transform Toolbar

The View Transform Toolbar displays a number of options for managing your monitor's colorspace in Mari.

Note: You can toggle Color Management in the Project Settings Dialog. When Color Management is disabled, you can still enable the View Transform toolbar by clicking the / Color/Scalar icon.

View Transform toolbar when Color Management is turned on:

View Transform toolbar when Color Management is turned off:

Select a channel in the Channels Palette and use the toolbar to choose the view transform and edit the LUT etc. The color icon on the left is gray if the channel contains scalar data, otherwise it is color to indicate color data. (For a more detailed explanation, see Color Data and Scalar Data).

You can change the view transform's canvas colorspace using the dropdown list, and revert to the default colorspace using the reset button.

View Transform Controls

Control	Type	What it does	Notes
	button	Toggles on and off the View Transform. Also indicates whether you are viewing color or scalar data. - The data is considered as color data and is being color managed. - The data is considered as non-color data, specifically scalar data, and has no color management applied. Note: The View Transform scalar mode is automatically enabled when viewing nodes that connect to scalar streams of Multi-Channel nodes, Material nodes, or Shader nodes.	Click to toggle. See Color Data and Scalar Data for more information.
	button	Select an OCIO configuration file.
Input Colorspace	dropdown	Set the colorspace of the current channel or painting in the Input Colorspace dropdown. (This is remembered for each channel.)
View Transform	dropdown	The View Transform operation is applied to the canvas before it is displayed on the screen. It is typically used to convert from the working colorspace to your monitor's colorspace.
	button	Reset the View Transform colorspace back to the default as set in the Project Settings Dialog. If it's a color channel, the Color Monitor project setting is used. If it's scalar, the Scalar Monitor project setting is used.
	button	• Select a custom LUT to apply to the scene. • Clear the current LUT applied to the scene. • Set whether the GPU extrapolates the grid values or clamps to the maximum value of the LUT.
Component	dropdown	View the individual channels for the scene.
F-Stop, Gain	incrementer, text field, slider	Set the number of f-stops or the amount of gain correction applied before the view transform.	You can boost or reduce gain by entering a multiplier (exposure value), dragging on the slider, or adjusting the F-Stop value.
Gamma	text field, slider	Set the amount of gamma correction applied after the gain viewer process.	You can boost or reduce gamma by entering a gamma level or dragging on the slider.