The only supposed difference between a blue 1tb and black 1tb drive is the warranty.
There is no other difference. Infact the blue one uses a single 1 tb platter( which is considered more reliable than multiple platters) while the latest blacks have now started using the single platter for 1tb capacity.
There is no difference in performace for 1tb part the last time I checked. If the black is older version than the blue have slightly better performace. Until or unless something have changed. Also, I bought a WD blue 1tb for Rs3450 at the local market 4-5 months back.
Just correcting the info. The seller can ask anything he deems fit. No point arguing. It's upto the buyer smartness to interpret what price he actually wants to give.
But, the correct facts must be mentioned.
Consider it a free bumb.