Problem with going to colour once you have already made your mind up to stay with b&w everywhere else is, you will tend to start getting more and more colour once you have started, and before you know it, you may be screwing up the original work in the name of colour.
I don’t see why the red would look out of place at all, black and red are a normal healthy looking combination. But be aware, if it looks great, you may need to tint the others with colour. IMO
Good luck!!