By true colours, do you mean the colour representation under a particular temperature of white light?
No, by true colors, I mean the color representation under an equal energy radiator or the CIE Standard illuminant E, the color representation under the purest form of white light.
Here’s what wiki has to say about it:
Illuminant E is an equal-energy radiator; it has a constant SPD inside the visible spectrum. It is useful as a theoretical reference; an illuminant that gives equal weight to all wavelengths, presenting an even color. It also has equal CIE XYZ tristimulus values, thus its chromaticity coordinates are (x,y)=(1/3,1/3). This is by design; the XYZ color matching functions are normalized such that their integrals over the visible spectrum are the same.
Illuminant E is beneath the Planckian locus, and roughly isothermal with D55.
Illuminant E is not a black body, so it does not have a color temperature, but it can be approximated by a D series illuminant with a CCT of 5455 K. (Of the canonical illuminants, D55 is the closest.) Manufacturers sometimes compare light sources against Illuminant E to calculate the excitation purity.