In the AC world, black is hot, not ground. In the car world red is positive and hot. In the telecom world of -48VDC, what color code do you follow? You can use red for positive, black for negative, black will be hot and red ground. NO way to avoid confusing at least half the people all the time!

For the car, I have a set of safety jumpers that have a heavy connector in the middle and an LED on each connector. To use, the cables are pulled apart, each end clamped onto pos and neg, and when both LEDs light you know you have the correct polarity and it is relatively safe to connect the two cars by plugging the jumper cable back together. This also makes the last connection farther from either battery and any probable hydrogen buildup.