The are several RGB spaces that are formal color space standards. Each can be used in Capture One for color correction and when using color readouts for comparing with reference values supplied with reflectance charts (i.e., color targets). These include sRGB, specified by HP and Microsoft (IEC 61966-2-1:1999), Adobe RGB (1998), ProPhoto RGB (ROMM) specified by Kodak (ISO 22028-2:2013)б and ECI RGB v2 specified by the European Color Initiative.
One of these color spaces should be used when editing and using the Lab color readouts in Capture One. The color space profile can be selected using either the proof profile option or from the selected process recipe (verification required). Note that Capture One does not edit in this space, but it determines the color it would use if it processed the image to a file. When the process recipe option is being used to determine the space, it is this same space that is used when being processed for output. Therefore, the proof profile option should be used with some caution if an output file is required for further validation, in case it is processed with a different color space profile.
RGB color spaces vary in gamut, gamma tone curve, and white point or media white. The profiles used to describe those characteristics are open to interpretation by different color engines when converting to the Lab color space. While that is not an issue if you only ever measure RGB readouts in Capture One, besides taking care to match the RGB space of the chart’s reference values and the output RGB space, this can cause a mismatch if comparing the Lab readouts in Capture One with the color values in the output file using a third-party application.