Below is a smooth 24-bit transition between white and black. In Netscape - well, the less said the better. Netscape's ability to render this type of image is seriously flawed and has been for several years. Know your audience. Depending on they type of surfer your site is aimed at, you will have a pretty good idea of how much you have to religiously adhere to the web-safe palette.
Business people tend to have less well specified computers than home users.
If a computer is used mainly for word processing or spreadsheets, high colour depths and sound capabilities are not very important. Emotive aspects of colour. Apart from the more obvious 'attention seeking', or 'traffic lights colour-coding' uses of colour, its ability to stimulate emotions is of paramount importance. Colour can create moods and send subliminal messages to reinforce your communication - if used properly. In the wrong hands, it can just as easily turn people right off.