I think the male not colouring up could have two reasons
1 – he might be young, only just maturing. Some paros are slow in maturing. The female might also be young, so the courtship behaviour is not all that strong yet.
2 – The two ‘extra’ fish might also disturb his behaviour, one of them might be another male..
Again, I think the best way would be to give a potential couple the tank on their own, provide an attractive cave, – then it will probably show up more quick if something is going on.