Most Web designers quickly become familiar with the Web-safe color palette, a set of 216 colors that are common to both the standard Mac and Windows 8-bit color system palette. Since designing images that display equally well cross-platform is a high priority when your primary design work is for the Web, you may never have previously needed to consider what colors to use to optimize icons specifically for a desktop color palette "desktop safe" colors, if you will.
Luckily, limiting colors in your icons is much less of an issue today than it was in years past. The most recent Apple guidelines for creating Macintosh icons don't even refer to color palette limitations. Under Windows, color palette limitations in icon design are a consideration primarily for accommodating those users with extremely limited or outdated systems.
One recent project I was on that called for icon creation involved designing the user interface for a biotechnology company's new instrument. The device ran its own proprietary software, and all screens needed to share the same 8-bit color palette. In a case like this, icon editor software could be used to specify or limit the custom color palette that was needed. Just to be safe, I wound up creating a custom color palette in Adobe Photoshop, applying it to all the icons, and automatically saving the files again in Photoshop to ensure the custom color palette was properly used.