This is a hint for a solid color that can be used for caching rendered views. This should be the color of the background when there is a solid background color; it should be null when the background is a texture or translucent. When a device is able to use accelerated drawing (thus setting state_accelerated), the cache hint is ignored and always assumed to be transparent.

Must be a color value, in the form of "#rgb", "#argb", "#rrggbb", or "#aarrggbb".

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

[Android Documentation]