i actually experienced the same thing a while ago when i first got the car...a while ago being a year ago. my car is a 2000 LX Sedan...i think what happened is that the brake fluid is not leveled. since liquids contract when it is cold, it probably shrinks, when the car heats up, the liquid expands to the level it wants to read at. just so we're on the same page, the light that goes up is the same light that would normally go up when you pull your hand/parking brakes right? if so, just top your brake fluid a bit, don't overfill it, but a bit. yeah this only happens when its cold. nothing i would worry about, unless there is something else someone else can point out?