Black helicopters in Chicago

I was playing basketball at night with my friends and between the hours of 10:00 to 11:00 PM black helicopters started flying overhead. They circled the same area about 15 times in a clockwise fashion. The rotating wings produced a distinct "chopper noise" that could be clearly heard by everyone there. It contained red flashing lights while flying.

This is the second time I saw black helicopters. First time when I was at college in Champaign, IL. Men came parachuting down from them. This occurred during the economic turmoil last year.

I wonder how many dark colors look "black" at 11:00 pm? Darn near all of them maybe?

Could they have been some other color? Maybe dark olive green? Blue?

Ya practically any color helicopter would appear dark to blackish at 11pm, so really we have no idea what kind of helicopters they were.

Could have been med evac, police search, news, anything.

We would need decent quality photos to figure it out.