I just saw a golden stout, I thought that stouts had to be dark and use roasted malts. What does a golden stout taste like? The same as a stout minus the color?
These stouts my also be known as "Blonde" or "White" in additional "Golden". Supposedly the idea first came about in 2007, when it was joked that Stone should brew a Golden Stout, it being a sort of oxymoron. However, it appears that now it exists. Stone Brewmaster Mitch Steele decided to create it, a light colored beer which had the flavors of a stout,
“To achieve the qualities of a stout, we relied on our prior experience brewing with coffee to pull flavors from the beans without affecting the hue of the beer,” explains Steele. “As the beer warms and opens up, the chocolate adds another level of complexity and helps build the traditional flavors typically associated with dark beers. It’s been really fun to see a prank with questionable viability become a reality.”
While this isn't the only example, it's one of the more notorious ones that serves well to explain the idea as well as how the flavoring is achieved.
In addition to @john-m's answer about the modern white stouts which are paleish with coffee/chocolate flavors, there historically were pale stouts which predated our modern concept of stout as a dark beer with chocolate/coffee flavors.
Check Zytophile for some historical context. He goes on for a bit but the main takeaway is that from the early 1700s to at least the 1850's there are ads, brewing records, mentions in manuals, etc of "Pale Stout". Basically because:
For 150 years or so after the word stout first began being applied to beer it was used simply as an adjective to mean “strong”.
Also a little bit worth reading at Shut up about Barclay Perkins, though in this case the comments section is a bit more interesting than the body of the post, specifically this comment by Ron Pattinson:
What makes it a Stout? The brewery called it one.
What we think of today as Stout was originally called Brown Stout. A strong beer brewed from brown malt. Pale Stout is the same thing, just brewed from pale malt. It's a very 18th-century way of defining beers.
Like John M said, it's sort of an oxymoron. It is to stouts what a black IPA is to IPAs. It has similar flavor and mouthfeel to a stout, but it's the wrong color. Just like a pale ale can't really be black, a Black IPA still has the same hoppiness and lighter body of an IPA.
And like Sloloem mentioned, "stout" was originally a reference to the flavor, meaning a strong beer, but today is generally understood to mean a beer brewed with dark malts.
If you are talking about the Stone Stochasticity Master of Disguise, I recommend you get it and try it for yourself. It's excellent. I've had a lot of coffee stouts, and a lot of chocolate stouts, and in my opinion that one is executed better than any of the ones I've had.