The title sounds like a variation of the standard Dancing in the Dark, doesn't it? But I have a quite different matter on my mind however. It's something I learned during my journey to the Listening Centre in Toronto in 1999. And it's this: the awareness of higher frequencies is, for the singer, like having a bright light on in a room. You can see everything much more clearly. Colors stand out. Green becomes greener, red redder, while forms and shapes have depth, and shadows have contrast. Reduce the light, and colors become grey and muddy. Heck. It's even a rule in decorating. A house can stand day-glo colors if it is in the bright and blazing equatorial region, but will look out of place in Norway. There the colors have much more grey in them.
It's the same with vowels and vocal tone. Take away the higher frequencies in the singer's perception, and the voice loses its color and flexibility. Is it any wonder then, that the Old School teachers taught that depth of tone, and even head voice, was gained via closed vowels like /i/ which has these frequencies? Many Old School teachers taught their students to vocalize on /i/. Lilli Lehmann even turned this vowel into the cornerstone of her technique. Alfredo Krauss talked about it in a masterclass which you can read in this transcript.
Let's back up a second: did you click on the link to Dancing in the Dark and watch Fred Astaire and Cyd Charisse? You should, if only for the sheer glee of watching two masters of the craft. It was a nighttime scene, right? Ok. What color were they wearing? White, right? Would it have been easier to follow their images if they were dressed in black? Ah...no. I don't think so. Dark colors on a dark background? They would have been lost. No chiaroscuro in that. Here's the deal. Great art directors and voice teachers know this simple truth: If you want to sing with a dark color, make a romantic scene with your voice, you had better keep your vowels clear and forward, or your listener won't get the picture.
Want to sing full-on classical music? Find your day-glo /i/. Make it radically pure. Vocalize on it while thinking /a/. Turn the halogen lights on and sing! Otherwise, you are singing in the dark.