To calibrate a display, a standard color gamut is defined by the target chromaticity coordinates of RGB primaries in CIE 1931 color space, e.g. DCI-P3 and Rec.709. Due to lack of spectral information of such standard target gamut primaries, transformation of target color gamut from CIE 1931 color space to another color space associated with a different observer (defined by a different set of CMFs) is not possible. In this paper, we introduce a novel method for transforming target primary colors from CIE 1931 color space into a new target color space with improved color appearance consistency for typical observers. Our approach represents each primary with a simple spectral definition across the visible range. Results demonstrate that this spectral definition significantly reduces inter-observer variation, thereby offering a practical solution to cross-observer display color space transformation.