This is an expression used by
Brazilian children to describe
any
colour that they don't know how to define. For example,
some complicated compound of
green and
blue with a hint of
orange.
I don't know of any equivalent expression in English.
This was told to me by a friend of mine from Rio de Janeiro, so
it must be true. He didn't say whether
the ass in question is of the donkey
or arse variety, but I'm presuming the former.