Lightening bricks
If you want to lighten the bricks then there's a great trade secret that might seem a little odd! Take some milk or yoghurt and brush it onto the brickwork. Leave it to dry and it will instantly age the bricks.
Darkening bricks
If you want to darken the bricks so that they blend in with existing brickwork then it's equally easy. You can mix chimney soot or mud with some water and brush it straight onto the brickwork. Leave it to dry naturally and voila, your bricks have immediate character.