Unfortunately, you can't set the blinking property of a control with imported bitmap nor you can set its "Color" property. The bitmap fixes to color of the control and LabVIEW can't change it.
However you can always put a transpatenr boolean over a picture ring in wich you put the pictures for the different states you need (ON,OFF,BLINK). On the diagram you wire some simple code to intermittently show the blink picture when needed.
I hope that helps