Icons quite commonly have a transparent background, this collection was tested using a light grey or white background. Background colors have not been set in display pages to facilitate testing an icon against an intended background.
Warning - beware of expansionism. An icon is invariably smaller than the block partitioned on a drive, but this block is the minimum amount of space that can be allocated to a file. Those cute little icons you just downloaded once de-archived will consume far more of your drive than the sum of their bytes.
Tools for Iconography : Implements of construction, conversion,,,