The conventional forvm wisdom is to avoid dark trousers with odd jackets.
With a dark odd jacket (e.g. a navy blazer), the combination is condemned as lacking sufficient contrast.
With a lighter odd jacket, the combination is condemned on the basis that 'darker jacket / lighter trousers' works better.
But what low-contrast or light jacket / dark trouser combinations do people think work well?
My contribution: the low contrast blazer and greys can work very well as a formal and classical combination (despite criticisms to the contrary), but easy to foul up if the fine tuning is off:
Beyond low contrast blazers, despite Foo's explanation later in the thread, I think that Rubinacci looks pretty good here: