I guess I most associate singers voices with colours.
Anna Moffo for example has a lovely dark, purpley sound in her middle register, but when she goes into her upper register the colour doesn’t bloom, it becomes a sort of silvery, less luxurious colour which lets me know there’s not enough girare in her sound. When there is, a singer like Nilsson for example, the colour remains consistent but I begin to imagine it with a gleam, as if the voice is glowing. Oddly, I don’t associate male singers, especially tenors and baritones, with colour in the same way as women and bases.
Milanov’s sound is platinum, sorry Milanov but no, I don’t hear gold, but a lovely platinum with streaks of light purple and silver. Tebaldi is gold, but a light gold, edging more towards pure white gold at the top. Nilsson has a silver voice, but with shades of blue, especially in the upper middle. Callas is a special case, a black-purple voice with shades of blue, dark, dark reds and when singing softer it can be hued with rosy pink. Grace Bumbry’s is a very dark brown, burnished with gold. Simionato is a blue/silver not unlike Nilsson’s but with less brilliance and a softer blue. Barbieri is a dark purple which pales at the top and darkens into a deep purple/black at the bottom. Dominguez is deep red with orange and a gleam of gold especially towards the top, with some vibrant browns right at the bottom. Verrett is a deep brown/black with a streak of silver which becomes more prominent as the voice ascends. Clara Petrella is orange with yellows and reds and a faint silvery gleam. Ponselle is a very rich chocolatey, reddy purple.
As far as men go, Corelli has an orangey sound, with browns and faint strokes of gold, while Del Monaco’s is like gleaming steel all the way through, darker at the bottom, like silver paint mixed with black, but still with a gleam, and brighter at the top. For some reason I rarely see baritones with a colour, and when I do the association is not strong enough for me to write it down. Who knows why. Basses are a bit easier, Siepi is black with slight purples, Neri is a dark grey all the way through. Ghiaurov dark silver and Talvela a lighter purple with some greys and black. Tozzi is the most beautiful black/purple sound with hints of a more reddy purple towards the top, more bluey purples in the middle and more towards black at the bottom.