HTML and CSS design and build websites

Use GIF or PNG format
when saving images
with few colors or large
areas of the same color.
When a picture has an area that is filled
with exactly the same color, it is known as
flat color. Logos, illustrations, and diagrams
often use flat colors. (Note that photographs
of snow, sky, or grass are not flat colors,
they are made up of many subtly different
shades of the same color and are not as
suited to GIF or PNG format.)