Red colour

I think red color makes them angry and so they go ahead and attack red piece of cloth.

I think the second part of your question contains the answer of your first part of the question. Yes, bulls are color blind and therefore colors doesn't matter to them. The fact is that any movement in front of them could excite them to an extent of attacking others...!

I think Ajoy is correct.As red color is very deep and when it moves bulls get angry quickly.

I say to all of you that the bulls cant identify the colour.This is fact.

Thanks everyone to clear my information. I didn't knew that bull is blind.

This is myth. Bulls are color blind. See the link below:

http://dsc.discovery.com/fansites/mythbusters/db/animals/color-red-makes-bulls-go-ballistic.html

by this post today i got known that bulls wont be angry by color they just angry by the moving object. I think in films they show for special effect

Yes you are true that bulls can identify the colour due to angry with fear they attack us.