直接调用系统的颜色显示在网页上本来是件很好玩滴事，但是，也有个缺点，就是可用的色太少 比如Bindows在它的启动画面一点点应用。
=。= 上次本来想在某个产品上应用，结果给人BS了，原因是色不好看 囧rz
在css21 中 System Colors也有相关描述，CSS3还加了超链接的色，还有个flavor。
但是，要有浏览器支持才是硬道理，浏览器不支持，虾米都回家睡觉。
附各色显示效果，如果看不到文字部分就像刮彩票一半刮开看一下，其中，Background 这个在safari 比较神奇，是透明哦。
CSS2.1中的System Colors
ActiveBorder Active window border. ActiveCaption Active window caption. AppWorkspace Background color of multiple document interface. Background Desktop background. » test color:Background @aoao ButtonFace Face color for three-dimensional display elements. ButtonHighlight Highlight color for three-dimensional display elements (for edges facing away from the light source). ButtonShadow Shadow color for three-dimensional display elements. ButtonText Text on push buttons. CaptionText Text in caption, size box, and scrollbar arrow box. GrayText Grayed (disabled) text. This color is set to #000 if the current display driver does not support a solid gray color. Highlight Item(s) selected in a control. HighlightText Text of item(s) selected in a control. InactiveBorder Inactive window border. InactiveCaption Inactive window caption. InactiveCaptionText Color of text in an inactive caption. InfoBackground Background color for tooltip controls. InfoText Text color for tooltip controls. Menu Menu background. MenuText Text in menus. Scrollbar Scroll bar gray area. ThreeDDarkShadow Dark shadow for three-dimensional display elements. ThreeDFace Face color for three-dimensional display elements. ThreeDHighlight Highlight color for three-dimensional display elements. ThreeDLightShadow Light color for three-dimensional display elements (for edges facing the light source). ThreeDShadow Dark shadow for three-dimensional display elements. Window Window background. WindowFrame Window frame. WindowText Text in windows.
CSS3 新加的 User preferences for hyperlink colors
ActiveHyperlink Active hyperlink background. ActiveHyperlinkText Text of an active hyperlink. HoverHyperlink Hover hyperlink background. HoverHyperlinkText Text of a hyperlink in the hover state. Hyperlink Hyperlink background. HyperlinkText Hyperlink text. VisitedHyperlink Visited hyperlink background. VisitedHyperlinkText Text of a visited hyperlink.
flavor An accent color (typically chosen by the user) to customize the user interface of the user agent itself. User agents may default the ‘flavor’ color to the dominant accent color used on the physical machine/mechanism that the user is interacting with (frequently a mouse, keyboard, monitor and computer case, often just a laptop), if the UA is able to retrieve that information from the platform and machine. It is not expected that this value will make sense on all platforms and machines.
推荐本书：《Web标准设计》
