A bookmarklet is a tool formatted as a link. You bookmark the link by right clicking and choosing "Bookmark This Link" (or similar). Having done so, the tool will display every time you select the bookmark from your bookmarks menu (in your browser). In other words, once you have bookmarked the tool you don't need this page to use the tool - just select it from your bookmarks. To try, just click a link below.
These 16 colours are those that were originally supported in the Windows VGA palette.