Thanks again for the all the tips and suggestions.

It turns out we still had a leftover can of the paint used for the
siding, so we were able to just do a touch-up job ourselves over the
caulked areas, and the new paint seems to be blending in with the old
very well. We'll just need to hire someone for an hour or less to
finish up some areas that were too high for us to reach. Our realtor
even helped us with the painting.

I am planning on filing a claim with the Construction Contractors Board
and Better Business Bureau; there was actually more that went wrong
than just the white caulk... they left our gate open and now the dog
we've had for 11 years is gone, and also the contractor was extremely
rude, yelled at my wife, and called me lazy for not taking care of
everything myself. He is certainly not very professional.

Unfortunately, we didn't have a contract with the contractor. So, I'm
not expecting any kind of claim to go very far, but at least there's a
lot of people right now (realty agency, title company, neighbors, etc.)
that know about the awful job the contractor did and won't be using him
in the future. An attorney would be nice, but I think paying for an
attorney would just offset any kind of re-imbursement we might get.
Our realtor set up the job for us, and the siding contractor they
usually use was busy for at least three weeks, so they went with a
referal from that contractor. They checked to confirm with us first,
and it seemed reasonable at the time. But I have certainly learned my
lesson now; always leave money for repairs in escrow, and let the buyer
deal with it, and if that doesn't work, get a written contract for all
repairs!

--Matt