Not all hardware and software platforms are capable of supporting all color depths. You should consider the following when deciding what image formats you'd like to provide to your audience:
Video configurations may be limited in color depth do to capabilities, available memory, or video driver limitations.
Windows 95 does not display icons in greater than 16 colors. A desktop enhancement is required, such as Microangelo or the Windows Plus! Package.
Windows NT 4.0 does not display True Color image formats properly. Avoid True Color images if your audience includes NT4 users.
Some users may opt to set their icon color depth to 4-bit (16 colors) to reduce system resource usage.