As of this time, there is no established facts regarding the screen-used coveralls, as the original pair(s) have not surfaced for analyzation to this community. Many hypothesize they were "Big Mac" brand from JC Penney but other vintage brands show likeness, as well. The color, affected by Dean Cundey's different filters, varies throughout the film & has essentially become a personal preference. Many guess the color to have been navy, charcoal, olivewood or a variant of one those colors e.g. charcoal blue. Nick Castle's height has been purported as a slender 5'10" or 5'11", which one could guesstimate his size could range from 38R or L to a 42R or L, perhaps.
I hope this helps to answer your questions.
Until this moment he had hoped against hope that the entity he had pursued to this place was a thing of flesh and blood like himself, though deep in his heart he had known it would be otherwise