色彩的基本原理——正色和负色

大家都知道三原色RGB，即由红绿蓝三色可以组成任意颜色，显示器和投影仪等显示设备即使用了这一原理。此即所谓的正色(additive color)系统，直接发射一些颜色的光来形成影像。

与此相对的负色(subtractive color)系统，是通过吸收掉白光中某些颜色的光线来形成颜色，彩色打印即使用了这一原理。自然光一般是白色光，即包含各种颜色，打印在纸上的墨点可以吸收特定颜色的光，从而反射出来的颜色是它的补色。这种颜色系统所使用的原色是蓝绿（青）色、红紫（洋红）色、黄色和黑色(Cyan, Magenta, Yellow, blacK)，即CMYK。

从定义上讲，三原色是能够按照一些数量规定合成其他任何一种颜色的基色。为了确定三原色，你必须首先确切明确哪一种颜色是你正在使用的中间色。在上小学时，你可能就知道了三原色：红、黄、蓝，并且你现在用于展示的，仍然是红、黄、蓝三原色。但是如果你有喷墨打印机的话，花点时间把它的盖子打开，看看它的墨盒。你能看到红、黄，蓝吗？不能！你可能看到的是四种墨色：蓝绿（青）色、红紫（洋红）色、黄色和黑色。颜色的不同是由于你的电脑用的是正色，而你的打印机用的是负色。显示器发出的是彩色光，而纸上的墨则吸收灯光发出的颜色。更进一步的解释就超出了本文要探讨的范围。
除了发射与吸收光的不同之外，本文涉及的概念同样适用于正色和负色模式，出于本文的写作目的，我们仅探讨着正色模式的三原色：红、绿、蓝。

Computer monitors emit color as RGB (red, green, blue) light. Although all colors of the visible spectrum can be produced by merging red, green and blue light, monitors are capable of displaying only a limited gamut (i.e., range) of the visible spectrum.
Whereas monitors emit light, inked paper absorbs or reflects specific wavelengths. Cyan, magenta and yellow pigments serve as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colors. Like monitors, printing inks also produce a color gamut that is only a subset of the visible spectrum, although the range is not the same for both. Consequently, the same art displayed on a computer monitor may not match to that printed in a publication. Also, because printing processes such as offset lithography use CMYK (cyan, magenta, yellow, black) inks, digital art must be converted to CMYK color for print. Many printers now prefer digital art files be supplied in the RGB color space with ICC profiles attached. Images can then be converted to the CMYK color space by the printer using color management methods that honor profiles if present; this helps preserve the best possible detail and vibrancy.

参考：

 色彩学基本原理

Color Space Fundamentals