Someone has probably thought of this before but thought I would contribute it again . Take a paper towel and fold in four and squeeze some acrylic or poster paint onto it .Try and spread it out thinly so it doesn't clog up parts of the clear stamp. Now just use it as you would a stamp pad . This not only looks effective but means you have more colour choices especially if you don't have a lot of different coloured ink pads .wash paint off well after use.