I'm having a couple of tweed jackets converted to kilt jackets. But I don't have waistcoats that match them.

Is it a fashion faux-pas to wear a completely different color waistcoat under a jacket (assuming they compliment each other)? Or would it be better to just go sans waistcoat?

Usually in all the pictures I see of people wearing waistcoats under jackets, the two match each other. I can't recall seeing any where they aren't matched.