OpenCV Object Detection

[T]

Hi all.. what is the best way (using OpenCV) to go about detecting
objects by color?  Specifically, I need to detect multiple objects -
first, a main object (a coin), then multiple objects within that main
(green particles on the coin).  I'm finding lots of info about facial
recognition, but not much in the way of just detecting by color.  In
this case, the coin will always be silver and the particles contained
on it will always be some shade of green.

Accuracy is very important - which is why I figured detecting via
color would be the way to go.  My goal is to detect as close to the
exact size of the coin/particles as possible.  That said, if there are
more accurate ways out there I'm open to suggestions!  Thanks in
advance.