Just to reiterate: Red is ALWAYS positive, black is ALWAYS negative.
EXCEPT in the case of brushless motors or brushless ESC MOTOR leads ONLY. These are constantly switching between positive and negative. Sometimes you HAVE to cross the colors to get the motor running correctly and sometimes they're all the same color.
Other than that......
Always. Universal standard. DO NOT EVER confuse or cross them; even if it's a nonpolar setup (like an incandescent light bulb) it's still good to keep them straight.
Balance taps are another animal entirely but you don't have to worry about that.
Ain't it fun to get way more info than you asked for?