Official Purple is used on Northwestern University web pages as defined below. Use of this color is not required, except in the University logo. Official Purple: RGB: 82,0,99 Hexadecimal: 520063
Web-safe colors are not required for two reasons: 1) a miniscule percentage of users still use 8-bit monitors; and 2) a simple workaround exists: Use transparent backgrounds for images. Web-safe colors were advocated in the past because older monitors were only capable of displaying 256 colors.
"When you export your GIF, select the color that's going to be in the code next to it and make that transparent. Then set the BGCOLOR of both the cell in which you've placed the GIF and the adjacent cell to the same value. That color will now bleed through the GIF, and regardless of which color the browser shifts it to, it will be the same for both the GIF and the code-generated color, since really it's not in the GIF at all" (Lehn and Stern).
GIF and JPEG are the most common formats for web graphics. As a general rule thumb, their size should be small enough to load quickly (~25k). Total page load should be taken into account, however. According to Lynch and Horton, "at today's average modem speeds, pages designed for those dialing in from home should contain no more than 50 to 75k of graphics." PNG is an acceptable format, but only without a transparent background, which doesn't work on Internet Explorer.
Photography helps support one of Northwestern's distinctive qualities: "Locations on two beautiful campuses on Lake Michigan in Evanston and Chicago, and the Chicago metropolitan area, provide students and faculty a wealth of outstanding intellectual, professional, social, and cultural opportunities."