Color is a big issue from monitor to monitor. To be sure your colors look as close as possible to what you intended, stick with web-safe colors.
Web-safe colors are a palette of colors that all web browsers recognize and will display properly. Sending it other colors will cause it to make a "best guess" that can lead to unfortunate results. The color could be way off or be dithered with other colors to approximate. This is all most noticeable with broad areas of a single color. Photographs are usually fine.