Guess who doesn't read the thread!
Eh, I read it, but really, more than half the comments are OT, so what's the big deal? Nothing to see here, move along...
As for the matter of India Pale Ale (not 'Indian'), India was where they were originally destined to go, not where they were invented. They'd become popular during the British Raj with the Tommy Atkinses and the colonial authorities, because they suited the climate better than porter did (though the story that they were highly hopped mainly to preserve them for the long sea voyage is apparently a myth, or at least greatly overstated - porters of the time often had equally high hopping rates, though unlike IPA they were rarely dry-hopped). They were called 'pale' in comparison to the styles usually found back home at the time, but were still darker than the Czech Pilsener that arose a few decades later. The style was brought back to England by returning soldiers, and eventually evolved into the whole range of pales ales and bitters seen today.
Modern IPAs from the UK and Belgium (who picked up the pale ale styles in WW I, I gather, though IPA specifically seems to have only really caught on recently) tend to focus on balancing the hops with malt, and as with pale ales in general, are golden to amber in color (though it tends towards the lighter end of the color range). They generally use British or European hops, often just one type; EKG is the classic EIPA hop, while Tettnanger seems to be typical in BIPAs. The biggest differences in the two styles are the base malts - Belgian IPAs often use Pilsener malts and add crystal malts for color - and, more importantly, the yeasts, with BIPAs often have a certain amount of typical Belgian funk (though much less pronounced than with other Belgian styles). EIPA has a cleaner fermentation, but generally still has some characteristic fruity or caramel tones. Both are hoppy by local standards, but not as much as American beers tend to be. In the UK, there's some overlap between IPA and Extra Special Bitter, with IPA usually being a bit stronger but much hoppier than ESB.
American IPAs had existed before Prohibition but had come close to vanishing in the 1940s - for a long time, Ballantine was pretty much the only one with any wide distribution, and was known mainly for its unique flavor that came from aging in American oak (which has a much stronger flavor impact than French or English oaks). It became a revival style in the 1990s, and really took off in the past five years or so as a sort of backlash against the Belgian styles that were dominating the craft market from 2000 to 2010. AIPA is generally yellow to golden in color (but can be amber), uses a wide variety of hops with citrusy American strains being most common, is fermented with cleaner yeasts, and emphasizes the hops a lot more than those from the UK or Europe. Blends of different hops, especially in the aroma hops, are common and finding a good mix of hop flavors and aromas is a big matter for AIPA brewing.
Imperial IPA is a (mostly) American style that first appeared around 2008 (I think) and takes its name in comparison to Russian Imperial Stout; it's also known as Double IPA, though IME the ones with the double IPA label tend to be maltier (this could be just me, though). It takes the basic AIPA formula and pushes the envelope on everything, but where it really, really goes the extra distance is on hop rates - often right up to the maximum taste threshold for bitterness (around 120 IBU, IIRC) or beyond, with elaborate hop schedules and massive dry hopping loads. Its a love-it-or-hate-it, in your face style that tends to get highly polarized opinions. Even more than AIPA, it is a style that is subject to considerable experimentation.
So called black IPA, sometimes called India Black Ale or Cascadian Dark Ale, is basically an American IPA with added roast malts, and first appeared around 2010 if I am not mistaken. There seems to be a difference of opinion as to both the name of the sub-style and what degree of roast malt flavor it should have; a lot of brewers add the black malt at the end of the mash, to limit the roasted flavor, but others dismiss this as just food coloring and seek to have a noticeable roast quality in it, though never to the degree of a porter or stout. From what I understand, Brown IPA, Red IPA and white IPA are basically larger, hoppier versions of American brown ale, Irish red ale, and American wheat ale, respectively, though they are still evolving as styles so they may eventually have more defined style characteristics.