Barry wrote:

For whatever reason, last night a skunk decided to let fly against a
four or five square foot section of the white vinyl siding. A weak
solution of bleach water neutralized the odor in pretty short order, but
all attempts remove the yellow stain have failed so far.


I have no experience dealing with stains like that so this is nothing
more than a guess. What you need may be some kind of enzyme that can
break down biological stains. Call a pet store and see if they have
something for your problem.