Does it have to be a spray paint? I've used Delta's iridescent glass paint
in the past and know that it looks nice and goes on translucent (it IS glass paint, after all!). One of the white iridescent paints should give you a good translucent coat with a iridescent sheen. The only problem is that this paint can be a little hard to find, as it seems it's not available at some stores anymore. Martha Stewart's line of glass paints has been pretty good though. If you can't find Delta and see an iridescent glass paint from the Martha Stewart brand, I would give that a shot. This will only be seen when the light hits it though. Otherwise, it will just look like the color under it.
Otherwise, if there is an acrylic paint you think would work, you could always mix a drop of it with acrylic medium to get it translucent. This will basically just give you a very slightly pigmented version of the acrylic paint (you can tweak the ratio to your liking).
A reference would be helpful though. References are always helpful.