Shorthand hex notation substitutes 3-character color values for 6-character colors when each of the color channels is identical in an RRGGBB hex triplet. Shorthand hexadecimal colors can help optimize your style sheets, especially when combined with shorthand properties and grouping.
Conditional SSI let you deliver customized content to different browsers and platforms without requiring additional HTTP requests. With conditional CSS, you can include additional styles for modern browsers, without upsetting older ones.
Dithering uses existing colors to strategically change pixels to minimize apparent banding. While dithering increases file size, when used in combination with lossy compression and weighted optimization, dithering can allow lower bit-depths for GIFs and PNGs.