Pictures would make it easier to judge, and it depends on the rest of the outfit as well, but I would say yes with regard to black trousers, and maybe with regard to grey. For the grey trousers, the vest should either be identical in shade or else obviously distinct. Problems will arise when they are almost, but not quite, the same shade.
This; nothing else can be said except for maybe a fabric match/mismatch.
Thanks guys, I'll see if I cant get some pictures uploaded when I get home from work today.
The last three pairs are good to go. I would not wear the first combination. They are too similar, but not identical.
Thanks guys, appreciate the input!