cf/x has released a suite of inexpensive, pro-level plug-ins for iMovie. this is one them.
b/w coloriser is a plug that turns your clip into a monochrome clip - and you choose which color that is. it is basically the generalized version of the 'sepia tone' plug - except that it also supports all standard cf/x plug features:
all our plug-ins sport features such as specifying are of effect (i.e. you decide which part of the clip is affected) and picking effect colors directly from the clip. many plugs are free, most plugs range in price from USD 1.50 to USD 2.50.
all plugs can be downloaded for free and are fully functional. those plugs that must be registered put a reminder of that fact into the clip.