Took about 20 minutes to write some python code to search; takes about 1/3 of a second to try all 3x17x17 mutations and find at least one rectangle produced by each. So yeah, every single-point change "destroys" the solution.
That's interesting, last time this came around I started working though how to do it using a Sudoku style solver.
Step 1: If a solution exists it's going to have 4!(17!)^2 'mirror' images of the same solution. To avoid this problem we give each color a number and a specific ordering of the solution. Thus eliminating 4!(17!)^2 - 1 options.
Step 2: Based on the form that order takes we fill in the grid as much as possible. (Most of the top and side row).
Step 3: Start plugging in missing squares until you find contradictions. EX: If swapping a column gives a lower ordering it's not a valid solution.
I doubt there are any, but it probably wouldn't take that long to write a program to check...
EDIT: And after reading this, I'm starting to wonder about other ways to use this solution to search for others, such as swapping two colors:
http://bit-player.org/2009/17-x-17-a-nonprogress-report