There are five biggies that I run into a lot, though, and those are the ones that I always ask the bride to give me a physical swatch of the color, like a piece of paper or fabric, to show me what color she's talking about.
1. Pink. This is a color that can go very, very wrong. A little pink can go a long way if it's bright, and there's a big difference between pale baby pink and pepto bismol pink. Make sure you get verification of this seemingly innocent color.
2. Purple. Every cake decorator's nightmare, purple can fade and change color after you put it on the cake. Using powdered colors brushed on top can stop the color change, but you have to know what purple you want before you even do that. Is it a blue purple or a red purple? Better make sure...
3. Coral. This is a biggie. Coral can mean orange or pink, and since orange is a strong color it can be bad if you go the wrong way with this one.
4. Ivory. Ivory is a weird color. Real ivory is kind of a pale yellowish white, but as it gets older it gets yellower. I've also seen a grey version that people call ivory, so if you make it more yellow and the bride is thinking more grey, the color is going to stand out and look totally wrong.
5. Champagne. The king of all wrong color possibilities...Champagne is almost meaningless, since it can be either pink or yellow, and even orange or green. It's similar to ivory in tone, but it can go many ways, so get a sample to make sure you're going the way the bride wants you to.
And I'll add one more for fun, Gold. Gold can be yellow or pink or light or dark, and if the bride is picky you'd better find out which one she's using so that you can stay in the same range!