Do you believe for every grey tone there is corresponding blue such that there is a "perfect" match-id we can say that of course
I know that is good to use colors with similar saturation but in the above case, by definition, gray has no saturation at all and blue is saturated more or less.

My motivation for this question is that hotmail) has a light grey sidebar(left) and a blue top bar where the controls are depicted upon
selecting message.

It is a good combination and I wanted to know what are the "mechanics" behind it cause I am building a site where there will be light grey and blue top bar and
I want to find some good color combo to implement also.