It does not ignore, but just has no idea what is it in general.
Skin is not a magic wand. Skin is just a .properties files with some parameters. Richfaces components use such parameters for set particular styles.
If you want to skin other non-richfaces components, apply the required style to them by yourself.
What you need to do depends of how wide you want to use the skinability feature. If it is only about blueSky color, set background-color to the desire value.