Windows XP includes a technology the goes by the name of “Visual Themes”, or “Visual Styles”, or just “Themes”, which essentially takes control of the appearance of most interface objects to give them a fancier and more integrated look. (Windows Vista expands this concept by making the Themes considerably fancier, particular the "Aero" 3D Theme.) The most obvious way to recognize when Themes are active is to move the mouse over a button to see if the button changes its appearance (depending on the particular Theme, adding a highlight around the rim, possibly changing the color.) You will also notice that most controls have more rounded edges and often they are filled with a gradient rather than a uniform color. The standard XP Theme gray background color is also quite a bit lighter than the gray used in Windows 2000 or W9x (and in Windows Vista, is even lighter yet). Most people agree that Themes provide a more aesthetically pleasing user interface look, and even if people do not recognize the specifics, they can generally recognize instantly the difference between an “XP-Style” application and a “Classic Windows” application, with the latter being almost considered derogatory these days. (In fact, Vista shifts the point of reference, now referring to the XP Theme look as "Classic".)

There is, however, a downside to Themes, and that is that by taking control of the rendering of interface objects, we lose the ability to assign arbitrary colors to things. Although there are some exceptions, in order to maintain a uniform look, A-Shell ignores your color specifications when Themes are active. The primary exception relates to the foreground color of static text objects. If you want to override the color in all cases, including when Themes are active, then you must add 64 to the color palette number. For example, if 3 is magenta, specifying 3 for the foreground color of a text control will result in magenta in a non-Themed environment, but will revert to the Theme-specified color when Themes are active. To override this and force magenta in all cases, add 64 (+3 = 67).

See the topic fgc, bgc for another way to override the Theme color by specifying RGB color values directly.

The best way to disable Themes for A-Shell under XP is to click the “Disable Visual Themes” checkbox on the Compatibility tab of the Properties dialog of the shortcut that launches A-Shell.

There is a known bug in XP Themes relating to the Tab Control: the gradient fill of the tab body supports a maximum height of 600 pixels. If your tab body is higher than that, the portion beyond 600 pixels will be white instead of the gradient gray. (It’s a minor visual anomaly, will probably be fixed in an XP Service Pack, and in most cases can be avoided by not making the tab controls too large.)

Vista themes are supported by A-Shell for most control types. Note that the separate manifest file is no longer needed.