Generally if I need to do this, I put a binding on background colour similar to this (This is a 1 second flash). Make sure background fill is enabled.
if(
{TagToActiveFlashing},
case(
getSecond(now()) % 2,//Toggles every second
0, color(255,0,0), //Red
1, color(255,255,255), //White
color(0,0,0) //Black if neither 0 or 1
),
color(123,123,123) // color if not flashing
)