There are a million common hideous UI memes floating around. One of my least favorite is the use of the colors red and green as indicator colors.
First of all, about 8% of males (and 0.5% of females) are color-blind to some degree, and by far the most common deficiencies relate to ability to distinguish red from green. So this is a terrible choice of indicator colors: it would be hard to do worse. I spent an amusing few minutes Googling around to find out why these colors became standard for traffic signals, but concluded that it's probably anyone's guess—accounts vary substantially.
Secondly, "red means danger" is a complicated meme in our modern tech world. My Bluetooth headset has a red indicator on its power switch. It turns out that this means "Danger—the power is turned off!" I'd say that accidentally leaving the power on is a bigger danger than accidentally leaving it off, but really it's 50-50. Screening the power icons for "on" (IEC 5007, "1") and "off" (IEC 5008, "0") would have been a better choice. I just spilled coffee after finding that the lid button on my travel mug is marked with red for "Danger—the lid is closed" and green for "Go—the lid is open". Again, I would argue that the open lid is the bigger danger, but it's kind of 50-50. Best in this case would have been a design that makes it visually obvious whether the lid is open.
Bottom line: please get away from red and green as primary indicators of anything. As secondary indicators, they are probably fine. However, they don't convey enough of the right kind of information to be primary indicators, even to those who can see the difference. (B)