Banner Design Dos & Don'ts
C O L O R S
DON'T Make Your Banner Blend In
You want your banner to attract attention from the content of the page, so try using contrasting colors. Or shift the weight of the banner to the side opposite of whatever portion of the web page is design heavy. Or choose a distinctly different font.
DO Carefully Choose Images
Photos are made up of gradient colors that will degrade quickly during optimization, so consider carefully before using them. If a photo (or gradient bitmap image) is used, limit the space it occupies to as small a portion of the banner space as possible. Especially on animated banners, consider using clip- or line-art (with net-safe colors), which will hold up better when colors are stripped. Logos, as a rule of thumb, shouldn't occupy more than about 10% of the banner space, unless the banner is strictly for branding (logo exposure) purposes.
DO Use Bright Colors
Blue, yellow, and green banners generally provide higher CTRs than black-and-white. Use red as little as possible.
DO Limit Colors
There's an easily identifiable relationship between the amount of color in a banner and its file size, so to keep a banner from degrading, use as few colors as possible. Some color is necessary ... for branding purposes or to convey certain messages. Using web-safe, solid colors for backgrounds and text will achieve better results across browsers than complex blends or gradients.