"International" orange is considered to be the highest visibility color, especially against clouds or the sea.
Not sure about Z-Foam.... I suspect its related to EPO. You'll have to do some testing to see what paints will or won't attack it. EPO is resistant to most paints and so you can spray with most rattle cans. Many foams are NOT resistant to acetone or other solvents and will melt or suffer surface deformation.
Clip a scrap of foam from somewhere that won't harm the model and try the spray paint you want to use on the scrap. Apply it extra heavy and you'll find out quickly if the foam will survive.
If all else fails there's the Krylon "H2O" paints which are water based latex n a spray can. If you use that you'll have to apply very thin coats several times as it likes to run badly if applied for one coat coverage. Or you can get an airbrush and use water based acrylic paint.