Hi dannac
I think from memory for Sticker Sprays like that, that produce specific multi hue marks, you first need to set your “base” colour (for want of a better term!) in the Colour Panel to pure red, i.e R=255, G=0, B=0 for the effect to work “correctly”.
But as you have found, selecting other base colours will give you differing results depending on the base colour used.