Save by getting your polymorph and colour pellets in one package. Includes your selected quantity of standard white pellets plus 5 grams of each colour (red, yellow, blue, green, black). 5 grams doesn't sound like a lot, but it's enough to colour 1kg of polymorph. A little goes a long way.
To mix the colour, simply drop a few pellets in with the standard polymorph while heating. Mix it together and knead it thoroughly to combine.
Different coloured pellets can be combined to create a multitude of colours.