Hey there, kanishk raj!
@jimthenagual is right to the point.
In addition to what he already mentioned, I'd suggest you to take a look at WD Black's product page on our website.
There you will find all the features and advantages of the Black over all the other drives that you've mentioned in your title.
Basically what you need to know is this:
WD Black - Gaming and high-performance PCs that are using demanding software applications. The 5-year warranty is also a big plus to what the WD Black has to offer.
http://products.wdc.com/support/kb.ashx?id=MZyNnL
WD Blue - Solid & reliable for all computers, mostly used as an OS drive and as an additional HDD with an SSD for boot as Jim already said. WD Blue is not high on capacity though.
http://products.wdc.com/support/kb.ashx?id=tL8Pjk
WD Red - This is our NAS/RAID drive, that can take a huge workload and is testing in 24/7 environments. However all its features would be invisible if it's working as a standalone drive in your computer.
http://products.wdc.com/support/kb.ashx?id=ioqXsO
WD Green - Is our storage drive. It offers great capacities, though it's speed is not like the Blue & Black. It's mainly used as a secondary storage or put in external enclosures and used as a backup HDD.
http://products.wdc.com/support/kb.ashx?id=CcDDX5
Hope this answers your question!
Let us know if there's anything else!
SuperSoph_WD