Next mix a batch of thickish pollyfiller in a pot. Now pour the first layer of pollyfiller into a second pot and add some food colouring. Then pour the pollyfiller into the bulb, wash out the pot and repeat with whatever other colours you like.
To get the coloured blobs use a stick and prod the colours to the side of the glass. Once their if you make small circles with the stick it spreads to a nice effect.
Leave the polyfiller to get a bit thicker then insert a screw into the end. Leave the bulb to set and then your done!!! Just go screw it into sometning.
P.S: I left the glass from the bulb on for the nice shiny colour but you dont have to.
P.P.S: Please feel free to post pictures of your lightbulbs in the comments.