Brown sugar is not as sweet as white sugar.
It also affects colour hence brown sugar often being used in flapjacks and with stewed fruit (speciafically apples) to make the fruit look more caramelised
http://www.diabeteshealth.com/read/2008/04/28/26/is-that-soda-really-sugar-free-test-it-with-tes-tape-before-you-drink/ In this article a woman used Tes-Tape.