Little icons are usually done in flat colors, without shadows or gradients. Over white, normally icons are #CCCCCC default, and #999999 on hover.Over dark, normally icons are #999999 default, and #CCCCCC on hover. Depending on the context, some of those icons can also be displayed in #FFFFFF. The size of the icons can be changed proportionally. The sizes 16x16px, 24x24px and 32x32px are used for this. In some cases, the icons can also be displayed proportionally larger.