After the feedback i got i decided to try Spraypainting  i first experimenting with the remaining purple spraypaint I had left over from my glitches brick wall work on a small polystyrene hemisphere this created a smooth surface

As this was a success i then decided to buy red spray paint along with a whole polystyrene ball to try it on

I gave the ball two coats of spray paint this got rid of all the texture of the polystyrene and left me with a smooth red ball 

Finally I tried the spray paint on the wall creating a red square creating a consistsnt shade and without the brush strokes similar to the red balls.