To me, Bach’s music is not black and white; it’s full of colours. In my imagination each tonality corresponds to a colour. The WTC with its 24 preludes and fugues in all the major and minor keys provides an ideal opportunity for this fanciful fantasy. Let’s imagine that in the beginning there was innocence and therefore C-major (all white keys) is snow-white. The last piece of both books is in b-minor which is the key to death. Compare the fugue of Book 1 to the Kyrie of the b-minor mass. This has to be pitch-black. Between these two poles we have all the other colours, first the yellows, oranges and ochre (between c-minor and d-minor), all the shades of blue (E-flat major to e-minor), the greens (F-major to g-minor), pinks and reds (A-flat major to a-minor), browns (B-flat), grey (B-major) and finally black.
Of course this is a very personal interpretation and each of you may have a different opinion. Nevertheless if some of us happen to believe that music is more than just a series of notes and sounds, then a little bit of fantasy is welcome.