How to 'whiteOut' a tilemap?

I want to apply the 'whiteout' effect to my Tilemap.
It's that old skool game effect.
For instance when the player shoots my wall or something important (tilemap) - the whole tilemap flashes white for a couple of frames.
Cheers

 

have a full screen white image overlay everything, with canvas group component set it's alpha to 0 to make it transparent. when you want to make it 'flash', animate it so the alpha goes to 1 then 0 then 1 then 0 etc.

 

ok, that might work - it's a bit over my head

But, I have found another way to do this.

I created a new PNG that only contains white shapes on a transparent background. There are about 20 pieces that match the shapes of my level tilemap. Now I just create a new (white) tilemap above the level tilemap in the shape of the highlight. Then I set the alpha of the white tilemap in code.

It works