Who am I ? asks a very famous bright yellow powder from WWII

OK, Manhattan : Who am I ????

(a) In the popular imagination, I am often thought of as being a bright yellow powder (though if fact I might often be dark red or brown or even some other color).

(b) Oddly enough, it is exactly the same for me.

(a)  Some of my most important developments happened on Manhattan island, with strong Canadian involvement --- I think that was all about the word "Hope".

(b) Wow ! Me ditto,ditto,ditto !