Boy that sounds bad ! Should really be fixed as poser 12 is still sold, I am glad I skipped that version it never came out of pre release! 

The way it looks if it is an animation issue then setting the animation to 1 frame should fix it ... Or if you add a Node to the color, if it is Firefly you can add a Math --->> Color_Math Node on the light, set the color in there, you probably will not see it in the view but as soon as you render the assigned color should be Rendered

Amost forgot , you need to add the node to the Light Preview Color

I Can't test it in P12 as I do not have it but if this also does not work then P12 is having a big issue.