By careful use of color i n content, it is possible to cut load times fairly dramatically. While GIF formatted files can support a maximum of 256 colors, they can certainly use fewer as well. A black and while drawing only needs two color values. Many CAD drawings use no more than 16 colors. Reducing the number of colors in images has one other positive side-effect.
All computer systems have a fixed number of maximum colors that they can display.
To make matters worse, on many of these systems, the web browser will not have the abiliity to modify all 256 colors. When a 24 bit image is displayed on such a system, the display software has to quickly make a decision on which colors are important in the image, and which ones can be ignored. Sometimes the results can be quite different than the original image. By using the minimum number of colors in your image, you can guarantee that what the viewer sees will be somewhat close to what you intend.