Inner most ring is for interval

>M for major interval

> m for minor interval

Outer most ring is for Chords

> Green for major(big Roman numeral),

> blue for minor(small Roman numeral)

> red for diminished(small Roman numeral)

In your image,

> I, IV, V are major chords

> ii, iii, vi are minor chords

> vii is diminished chord.

For example,

If you select C major chord(I), the inner most ring shows you intervals related to chord I as 1,M3,5 and center ring with keys as C,E,G

If you select D minor chord(ii), the inner most ring shows you intervals related to chord ii as 1,m3,5 and center ring with keys as D,F,A