Windows icons often include both 16 and 256-color images in multiple sizes. Microangelo introduced support for True Color icons in 1998.
If you aren't including Windows XP images in your icons, we strongly advocate developing your hi-color images in True Color (even if you don't publish these images in your final icon resources.) There are significant reasons for this:
True Color images are not limited to a fixed palette of pre-determined colors. It is extremely difficult to edit images and import image data using a fixed 256-color palette. True Color does not require colors to be defined in a palette before they can be used in an image. It is exceedingly easier to build a color palette to support a finished image than to build an image and define allowable colors at the same time.
Microangelo's image editors provide enhanced drawing features that include the ability to create gradients and anti-alias processing to smooth the appearance of jagged edges. These features are only available when editing a True Color image.
The editors also provide high-quality color reduction algorithms that can create 256-color image formats from your final True Color images. You can easily create 256-color images from your True Color originals.
Windows does not recognize any difference between image formats that have 8-bit color or greater when it chooses an image from an icon resource. For this reason you should not include 256-color images and True Color images of the same size. Windows will always treat these images equally and choose the first hi-color image it finds.
The good news here is that Windows 95, 98 and Windows Me all support True Color images and a True Color system color depth flawlessly. The bad news is that the Windows NT shell has never properly displayed True Color icon images throughout all of its service packs. Although the shell in Windows 2000 appears to display TC icons correctly, a debugging environment shows that the Win2K shell generates heap errors every time it encounters a True Color image in an icon. Microsoft was aware of this months before the release of Win2K, yet the errors persist following the distribution and installation of the first Win2K service pack. For these reasons it is clear that True Color images must be avoided if the target audience may include NT systems.