I have what I call a yellow list which is a list of IP addresses of
hosts like yahoo, google, hotmail, aol, etc that send a mix of spam and
nonspam. The idea being that if you are yellow listed then don't check
any other list because if it was listed it would be a false positive.

So - the question - how would you write a rule to do a yellow list
lookup and if listed then bypass all other RBL tests? This would
increase speed and accuracy, and maybe get others inspired to build a
better yellow list than I have.