Yoy can pain them to suit you. However because they are 3 different colours, finding something that will make them all look the same will be difficult. From your descriptio I think you refer to wood panel fencing. With a single coat there is no realistic chance of them coming out the same colour, and with multiple coats the paint will quickly peel off and look even worse. Suggest it may be better (well it will look better) if you brighten the whole thing up by keeping three different colours - but obviously colours you like. You may well have to make the best of a bad job. Alternative is to paint them a very dark colour and then help disguise the panels with bright evergreen climbing plants, but this may take 3 or 4 years to achive.
Good luck