The condition where two color samples, with different spectral properties, produce the same color sensation under certain viewing conditions, and a different color sensation under different conditions.

For example: two colors match each other under one light source, but not another. Neutral tones may appear greenish, reddish, or blueish at different gray-levels.

This phenomenon where two colors appear to match under one light source, yet do not match under a different light source is called metamerism. The two such colors are called metemeric pairs. It's when you buy black socks and you go outside and now you notice that they are blue or black. The look different in the sun light that they did in the store. Think about it, the store has its own lighting. Our world is color managed and we don't even think about it, until something looks wrong to us.

Lighting is an extremely essential part of our world and they way stores use lighting for displays. Everything we do in color management, inks, dyes for clothing these are all metemeric matches. It's not a true natural color, but rather our eye interprets to make those things that aren't really pure color and imperfect look like pure color. This is why we can produce a blue, by mixing some magenta and cyan...This is also why blues in print, often look purple and not the blue you see on your screen.

Your screen is a true blue prosperous. This also explains why when you produce a print in your shop and you do all you can do to color manage and the print comes out looking great. You ship it off to the tradeshow and the customer calls, complaining to you saying that the logo color is all wrong. In the tradeshow hall, the print is now under a different lighting condition. The print is hung under lighting such as mercury vapor or metal halide and now it looks completely wrong.In our color managed world, have you ever come to a stop light and noticed that the green isn't quite right or when they started using LED lights, you noticed a difference. You notice because stop lights have been the same color, for as long as you can remember.

If fact, they've been the exact same color since they were invented. Now the longevity you can get with LED made the switch over the new standard. A funny thing is, I would bet there are teams of people working on how to get LED lights to simulate and get back to the original standard.Have you ever noticed that when you're at the meat counter or butcher and you select choice meats form the counter? Then when you get it home, it looks a little gray? The lighting in the case is meant to give off a warm magenta (using florescent tubes).Look at the super stores, lighting over the food, even in the bakery sections are different than the clothing sections within the same store. This is no accident.