I think this might be what my mother was talking about when she used to tell me that something was "sky-blue pink with yellow spots"... Paul tells me that he's never heard that expression before, but I used to hear it all the time when I was growing up, usually just after I'd asked my mother a particularly silly or overly inquisitive question, or one she just really didn't feel like answering.
Mothers have all kinds of clever ways of deflecting difficult or irritating questions (questions like "What's for supper???") - do you remember any from your childhood, or do you have any that you like to use on your own children?