Michael, such an option would be interesting, but at present it is serving the same purpose that hyperlinks being another color than the rest of the text on a webpage and changing colours when you hover over them serve.
With synths, it is even a little trickier, because you almost always have multiple overlapping photos. If no graphical cue is given as to which one you are selecting, how do you know which one you will be clicking on? I'm not trying to shoot you down, but rather interested in knowing if you have any concrete alternative solutions.
I think that more than anything, the Photosynth team, in wanting Photosynths to grow in popularity, probably wants a reliable experience for the average user. If the average user is accustomed to using the white frames to navigate and comes to a synth whose owner has switched such accenting off, will they really be savvy enough to find out how to turn them back on?