On researching the term "amber gambler" I have come up with a bumper crop of three meanings. Without further ado:

The traffic light explanation
Depending on where you live, the colours you see when you approach traffic lights can mean very different things. For instance, here in the UK, when you approach a set of traffic lights and it changes from green to amber it means you have to PANIC. Most people will accelerate if they think they can get through the lights before they go red. But it's a game of chance. Can you see where I'm going with this? "Amber gambler" is not just the person that goes for gold and tries to get through the lights. It's much more. It's the phrase you shout to shame the naughty motorist from the lofty moral position of the passenger seat. To grind salt into the gaping wound of shame, the line should be followed up with "How can you live with yourself?" in your best primary school teacher's voice. Tut tut.

The boozy answer
No matter what the question is, a pint of ale is always the answer. And this is a fine case in point. Amber Gambler is the trade name of an American Pale Ale made by the Holy Cow! Brewing Company of Las Vegas. According to the schpiel on their website (see below) it's 5 percent alcohol by volume and was a Gold Medallist at the 1993 Great American Beer Festival in Denver, Colorado. That's the same Denver where Coors is made. Forgive me if I appear sceptical ;).

X-Files mumbo jumbo
If you believe UFOs are extra-terrestrial lifeforms and get all excited at old cinefilm footage of flying dustbin lids, then read on: this definition is the one for you.

According to my secret government sources, "amber gambler" is a name given to the amber balls of glowing light seen by some in England in the 1960's, the decade when psychedelic drugs and sci-fi television shows hit the British mainstream. Draw your own conclusions. Further information I received in an envelope marked "TOP SECRET" slipped under my door suggests that amber gamblers are most often seen at the horizon and that sightings can last upto several minutes.

Ratebeer - http://www.ratebeer.com
Holy Cow! Brewing Company - http://holycowbrewery.com/beers.htm
About.com - http://ufos.about.com
Lunar Ace - http://www.lunarace.com/ufo2.html