[exim] Your Opinion about how to set up a DNS list

I'm doing something unusual and hope to make the service public soon.
I'm going to provide not only a DNS blacklist, but DNS whitelists as
well and my new concept - yellow listing.

So - I could make it a single DNS call where you look up
list.junkemailfilter.com and the result will return a different value as
to if it is black or white or yellow. You will have to check your
results to determine what to do with it.

or ....

I can have separate lists where if you read dnsbl.junkemailfilter.com
for the blacklist and dnswl.junkemailfilter.com for the white list. This
looks cleaner but if you use them both you make 2 calls instead of one.

So - vote - which way should I do it?

Here's the logic:

You test for white listing - if listed - no spam filtering - the host is
100% clean.

You check for yellow listing - if listed then the host is know to send a
mix of spam/ham and you skip all other blacklist tests.

If not listed on the above lists you check the blacklist and all your
other favorite blacklists and if blacklisted you boune.

If none of the above you let Spamassassin figure it out.

But - my original question. One call for everything or more than one?