A back or dark sound is one that is created more towards the back of your mouth close to the throat. Bass voices have differing qualities as well. The higher overtones allow the voice to project to the back of the room, and the warm tones add color and contrast making for overall beautiful tone quality. In reality, one way this can be achieved is by changing the resonating cavity (e.g., singing through the nose), but in most contexts that isn't preferable. Classical singing tends to seek a darker tone, while pop and rock is going to be a brighter tone. Bright/Light – Higher overtones are created and amplified. Your mouth and the way you use it can vary the tone that is projected from your voice. This voice resonates toward the back almost going "down" the throat. Some singers sound heavy and dark when using too much vocal weight and some singers sound light and disconnected when using it. Bright sounding ones, or dark sounding ones? Because vocal weight can also involve taking one register mechanism too high in pitch, the voice can often sound white and colorless if the larynx rises. A bright tenor can be either annoying or exciting, depending on whether the voice has sufficient body; Corelli's voice, for example, was thrillingly brilliant but also full-bodied. I am a baritone (mid way between bass and tenor) but I have a bright baritone voice… Warm/Dark – A warm voice has lower overtones. (A heldontenor is the tenor equivalent of dark beer.) This extreme sounds very "cartoonish." There are some really nice sopranos who have bright voices, for example, Mado Robin, and others like Renée Fleming, have a lot of darkness to their voice. Well-Balanced – A well-balanced voice has both bright and warm qualities. In classical singing, vocal tone is referred to as Chiaroscuro (may not be spelled correctly) which means Light/Dark. Strictly speaking, "bright" means a higher ratio of high partials to fundamental, while "dark" means more fundamental and low partials. A certain amount of brightness is needed in any voice, but especially in low voices, to avoid dullness. Buffo is brighter for more comic roles, bosso profundo is a very deep often sinister sound and bel Canto is a voice that is open. An extreme version of it would be what I refer to as the "Kermit the Frog voice."