The tone quality that you choose to use for singing is dependent on what vocal technique you can comfortably sing with, what the demands of your target genre/(s) are, what your audience or audition judges are expecting and of course your own style as a vocal artist. Sometimes, all these things DO line up with speech. For example, a country singer may have always grown up with a country accent. Other times, it doesn't line up. For example, I once taught a Korean foreign exchange student how to sing with a country accent because he loved country music and was curious to develop the country twang.