Actually we have one that probably looked exactly like him, 'cept our guy (Frost) has very faint teardrop and tail bar markings. Here's a pic of him and baby Mongo I had posted some time ago in a different thread.
As for the guy you saw I really can't say for sure what mutation he was, but there are Solid white males.
http://www.efinch.com/species/whitzeb.htm I'm going to guess the male you saw had a beak that was on the reddish side. As for Frost, after discussing it over with individuals who are far more knowledgeable than myself, we've come to the conclusion that he is a dilute Florida Fancy / CFW mix. Going more by the chicks that he has produced than by his actual appearance. He has given us a pile of Single Factor FF's (males and female) along with several CFW hens, as well as one male Double Factor FF thus far. And all have been with different hens. The one time we had him paired with a solid white hen, they produced a clutch of three solid white birds, two males that also had their daddy's bright red beak and a white hen with very faint tail bar markings.
The thing with Solid whites is, as Roy Beckham explains on efinch, (and as was very eloquently explained by Candace once on here) some of them are actually birds that are just over pied. So the only way to know for sure their true mutation is to breed them and observe the results.
In addition to being a very handsome fella, our Frost has the one of the sweetest dispositions. He along with most of his kids are very easy going and get along very well with our other zebras. He's starting to get up their in years now, we've had him for over four years, and remains one of our favorites. It's a shame you weren't able to snatch the handsome guy up, but we certainly understand what you mean by a lack of cage space.
30+ Zebra Finches (The actual number constantly changes) 2 Rabbits (1 Mini Rex, 1 Dutch), 1 Grouchy Old Fart, and 1 Dang Redhead
