In my previous version of FMP (i didn't upgrade since 10.5) I was able to create coloured radio buttons without the sorrounding line around the dot by setting the line weight to 0. This way the radio button was completely invisible when it was not active. When it was active, there was only the "dot". The dot colour was dependant on the line colour, and this worked even when line weight was 0. This little trick allowed me to easily create "traffic lights" to indicate different warnings etc.
In FMP 12 it seems that when I set the line weight to 0, the dot will always be black. I can only get a coloued dot, if I have a visible line (line weight > 0). Of course I can hide the line around the dot with a background-coloured circle, but this might not be very elegant when zooming etc.