In the U.S., the last (or fourth) Thursday of November was declared a national day of thanksgiving. It's been this way for a long time.
The phenomenon of Black Friday has gained traction much more recently as Christmas has become more commercialized.
I can remember (I think it was about 25 years ago), when I heard for the first time that the Friday following Thanksgiving Day had become the single biggest shopping day in the U.S. (Evidently, more and more families thought a day of shopping seemed like a good follow-up to a day of feasting.) I first heard this fact from my sister-in-law, who announced it as novel bit of trivia. I don't recall hearing that day called Black Friday, though, until relatively recently - with "black" referring to accounting sense of the word.
I make this distinction between the longstanding tradition of Thanksgiving vs. the relatively recent phenomenon of Black Friday because of your opening remark:
In the Western countries like USA and Canada, there is a shopping fest(festival) called Black Friday, I wonder why the word 'black' is added to it?
Even more recently, Black Friday is followed by Small Business Saturday (where consumers are encouraged to buy from smaller local stores, rather than "big box" chain stores) and Cyber Monday (where office workers allegedly continue their holiday expenditures by shopping on-line using their work computers). Really, though, these nicknames all seem to be driven by the commercial sector, with retailers using cutthroat gimmicks as they compete for consumer dollars. So, this isn't really an official, long-established festival, but more like a recent phenomenon. Only time will tell if these terms will stay entrenched, or be replaced down the road.
@CopperKettle edited my post maybe now it is more explicit – Dragut – 2015-12-04T11:53:37.743
In the USA (where the custom originates), Thanksgiving is a celebration which takes place on the 4th Thursday in November. Many (most?) people in the US get the Thursday and Friday off work. Since the actual celebration is on the Thursday, I guess many of them started going shopping on the Friday. The shops started competing for the extra customers by putting on sales, and there you have it, what is now called Black Friday was born. As to why it's Black, I have no idea. – Joseph Rogers – 2015-12-04T11:54:17.753
I have no idea if it's relevant or related in any way, but every other instance I know of where a day is called "black" refers to a day on which the stock market crashed. eg Black Monday occured in 1987 at the start of a worldwide recession. – Joseph Rogers – 2015-12-04T11:57:38.757
@JosephRogers when the stock market crashed? – Dragut – 2015-12-04T12:00:20.857
By the way, 'green' is evil! – Maulik V – 2015-12-04T12:01:08.410
sorry for the jargon, when the value of stocks and shares dropped suddenly – Joseph Rogers – 2015-12-04T12:01:23.937
. . .and in the UK, 'Black Wednesday', described in Wikipedia: In politics and economics, Black Wednesday refers to 16 September 1992 when the British Conservative government was forced to withdraw the pound sterling from the European Exchange Rate Mechanism (ERM) after it was unable to keep the pound above its agreed lower limit in the ERM. – peterG – 2015-12-04T17:34:38.600
We have good answers here; however, questions about etymology might better be handled at EL&U.
– choster – 2015-12-04T19:41:43.6601
It was asked in EL&U before: http://english.stackexchange.com/questions/93365/origin-of-black-blue-friday
– ermanen – 2015-12-04T20:30:57.013black is simply a color. it can mean all sorts of things, depending on the context. sure, usually in fiction it's used to represent something dark or foreboding, but it doesn't have to. it's just a color. – user428517 – 2015-12-04T20:43:19.813
Attributing negativity to a color depends on the culture you are in. Serious issues can arise by being ignorant to that, as in some cultures western roles of colors black and white are reversed. – benjamin – 2015-12-04T21:04:58.480
"everybody is happy, everybody wins!" Wow, that's one way to look at rampant commercialism I suppose – Lightness Races in Orbit – 2015-12-05T17:40:44.510
I always thought it was because fighting through the crowds of other shoppers was such a horrible experience. Urban legend says that there are often literal fights when the stock of particularly popular items starts to run low. (I have no idea whether that has any basis in fact.) – Harry Johnston – 2015-12-06T00:55:20.937
@HarryJohnston: it's more than urban legend that it happens, you can find some footage on news websites and so on. Current top hits on my search relate to an incident in Kentucky. Of course, without a more disciplined investigation one cannot rule out reporting/confirmation bias, since one assumes that there are fights in stores anyway from time to time, quite possibly as often as every day across the whole US. – Steve Jessop – 2015-12-06T01:09:35.257