System Colors
System—or logical—colors differ from standard colors in that the actual RGB color is determined from the settings on the machine.
For instance, if you want a dbForm to have the same background color as other Windows controls that accept user input, you would set the color to clWindow. This color is usually white, but by setting it to clWindow, the color will automatically change whenever the user changes the colors on their machine. If you had set it to the clWhite standard color, it would always appear white, regardless of the colors configured on the machine.
All the system colors have symbols representing their usage. Use clWindow when you want to use the color known as "Window" in the Windows configuration; similarly, clWindowText maps to "Window Text" and clBtnFace maps to "Button Face," which is the color used by Windows for all 3-D objects.
List of System Color Symbols
clScrollBarclHighlightclBackgroundclHighlightTextclActiveCaptionclBtnFaceclInactiveCaptionclBtnShadowclMenuclGrayTextclWindowclBtnTextclWindowFrameclInactiveCaptionTextclMenuTextclBtnHighlightclWindowTextcl3dDkShadowclCaptionTextcl3dLightclActiveBorderclInfoTextclInactiveBorderclInfoBkclAppWorkSpace