Why the intervals are to be given the numerical values of semitones?


There are two methods of measuring the interval in music: value of basic scale steps (major/minor) and value of octave semitones.
Supposing we were analyzing only the musical scale, the terms "minor third" and "major third" would be more appropriate. However, if all the elements are to be taken into account, their order should be mathematical, therefore in semitone terms minor third has the value of 3 semitones, and major third of 4 semitones.


Why the diagram represents less colours than the rainbow colour count?

Why a note can not correspond to a colour?

What is a consonant chord and consonance intervals?

Why the interval of 3 semitones is compared with the blue colour and not with yellow one, for instance?
How the multitude of colours we see is expressed in music?