OK, we can use "In some color spaces, the primary colors used are not real colors, in the sense that they cannot be generated with any light spectrum."  And please use spaces after your periods and commas to make your text more normal and readable.  I'm not sure what you're saying about "stimulus and reaction", or in what sense tristimulus values are "unsuitable"; they are a quite different from an HSV description; nonlinearly related; does that mean "unsuitable"?