The standardized OpenFX1 plugin interface used by the Colour Look and Feel does not explicitly provide information or facilities to obtain the particular RGB color space passed onto the plugins. The standard only specifies that the RGB data is linear but no further tone curves are specified.
As such the Colour Look and Feel allows nodes to accept XYZ as well as RGB data of varying color spaces for their inputs and outputs. This input and output color space can be selected for each node individually and is set to sRGB by default.