The rendering space is the working color space in which the rendering calculations are performed. It is also the color space of the rendered output (unless you apply an output transform). When color management is enabled, 2D texture files and other images get converted from their input spaces to the rendering space automatically. You can set the Rendering Space of a scene in the Color Management preferences .
When using the default OCIO v2 color management system, the rendering spaces that are available depend on the configuration file used by the scene. Only the spaces that are defined in the configuration can be used. Some configurations may assign a specific space to the rendering role — in such cases, it is the only rendering space that can be used.
Even if the rendering role is not used, the author of the configuration can limit the color spaces that are available to select for rendering by using the categories attribute of color spaces. If these are used, Maya includes any color spaces that have the category working-space and the encoding scene-linear.
The configuration files that are installed with Maya are named config.ocio and are available in subdirectories of resources/OCIO-config/ in the installation location. They all have the same rendering spaces, as does the older color management system known as SynColor. However, your project or studio may be using a different configuration with different spaces available.
It's always best to select the rendering space when you first start a project or scene. The color values defined by color controls, including solid colors and ramps, are treated as untransformed rendering-space values. If you change the rendering space later, the resulting color will be different. This is because the color represented by a set of values depends on which primary colors they refer to. For example, the color represented by [0.2, 0.6, 0.4] is different when using the sRGB primaries as compared to the ACEScg primaries.
The mathematics of lighting and rendering assume that the color-space encoding is linear, so it is best to choose a rendering space that is linear. All the rendering spaces available in the configurations installed with Maya are linear.
The ACEScg color space is part of the ACES standards, and is designed to be appropriate for computer graphic operations like compositing and 3D rendering. It encompasses both the Rec-2020 gamut and the DCI-P3 gamut for a range of white points. This is the default rendering space used for new scenes.
ACES2065-1 is an extremely wide-gamut color space. Its advantage is that it can represent any possible color. Its disadvantage is that it can easily produce out-of-gamut colors, and in addition can be unintuitive to work with.
The scene-linear DCI-P3 D65 color space uses the same primaries as a DCI/SMPTE "P3" reference projector, but with scene-linear color values and the D65 white point. The advantage of using this color space is that it can represent all the colors available on a modern projector. In addition, there is little risk of producing colors that are out-of-gamut for a projector, which might cause unpleasant surprises if the content is ever viewed in the future on a device with a wider gamut.
The scene-linear Rec.2020 color space is similar to scene-linear DCI-P3, but for UHDTV or HDR TV rather than digital cinema. The standard for HDR TV is actually Rec.2100, but it uses the same primaries. Note that because the Rec.2020 primaries are on the spectral locus, there are virtually no actual displays that are able to accurately show the full gamut of colors.