I'm going to a wedding soon, and I bought a black blazer from Zara, I want to wear a roll neck jumper with it, what colour would you say is best? I saw this picture of a model wearing a dark grey/black suit and light blue jumper which I really liked, but not sure if blue jumper would seem right? So suggest some colours please people! Links would be even better 
Also, another thing, I didn't buy brand new trousers and will just wear the blazer with a pair of black trousers I already have, but the colours are ever so slightly different and don't match 100%. Is this a big no-no or ok to wear blazer and trousers that are slightly different shades.
Thanks guys

Also, another thing, I didn't buy brand new trousers and will just wear the blazer with a pair of black trousers I already have, but the colours are ever so slightly different and don't match 100%. Is this a big no-no or ok to wear blazer and trousers that are slightly different shades.
Thanks guys