There will always be a colour issue when mixing different makes of armour. Some will match better than others but will never be a perfect match. I would have thought that the bells being a different material would not help either. Even by getting new AP bells there is no guarantee that the colour will be the same as each batch of plastic is a slightly different colour. Mt suggestion is to contact AP and see if sending him a small piece of your armour for him to try and match would work.
Rob.