For more information about the use of color and how it is used for interface elements, see Chapter 13, "Visual Design."
Base the color properties of your interface elements on the system colors for window components, rather than defining specific colors. Remember to use appropriate foreground and background color combinations. If the foreground of an element is rendered with the button text color, use the button face color as its background rather than the window background color. If the system does not provide standard color settings that can be applied to some elements, you can include your own interface that allows users to customize colors. In addition, you can provide graphical patterns as an optional substitute for colors as a way to distinguish information.
Note
For more information about the use of color and how it is used for interface elements, see Chapter 13, "Visual Design."
The system also provides a global setting called High Contrast Mode that users can set through the Windows Accessibility Options. The setting provides contrasting color settings for foreground and background visual elements. Your application should check for this setting's status when it starts, and whenever it receives notification of system setting changes. When set, adjust your interface colors based on those set for the high contrast color scheme. In addition, whenever High Contrast Mode is set, hide any images that are drawn behind text (for example, watermarks or logos) to maintain the legibility of the information on the screen. You can also display monochrome versions of bitmaps and icons using the appropriate foreground color.
Note
The GetSystemMetrics function provides access to the SM_HIGH-CONTRAST setting. For more information about this function, see the documentation included in the Win32 SDK.
Another important way to provide for visual accessibility is to allow for the scalability of screen elements. Sometimes, this simply means allowing users to change the font for the display of information. The system allows users to change the size and font of standard Windows components. You should use these same metrics for appropriately adjusting the size of other visual information you provide. For your own custom elements, you can provide scaling by including a TrueType font or metafiles for your graphics images.
Note
For more information about the system metrics for font and size, see Chapter 13, "Visual Design."
It may also be useful to provide scaling features within your application. For example, many application provide a "Zoom" command that scales the presentation of the information displayed in a window, or other commands that make the presentation of information easier to read. You may need to add scroll bars if the scaled information exceeds the current size of the window.