On the back of your personal computer are colorized audio jacks. They may or may not be labeled. The color coding is a fairly standard convention used by most personal computer manufacturers. Use the illustration below as a reference.
The color code standard is part of PC 97, PC 98, PC 99, or PC 2001 specification introduced by Intel Corporation to help simplify the setup and use of computers for consumers. Specifically, PC 99 gave us a color code for the various standard types of plugs and connectors used on PCs. This color code was gradually adopted by almost all PC and motherboard manufacturers. Some of the color codes have also been widely adopted by peripheral manufacturers.
Sound card color code: ---------- ---------------------------------------------- Color Connector Lime Green Line-Out, Front Speakers, Headphones Pink Microphone Light Blue Stereo Line In Orange Subwoofer and Center out Black Rear Surround Speakers for 5.1 and 7.1 systems Gray Middle Surround Speakers for 7.1 systems Gold Midi / Game port (Joystick)