If you just want the floor tiles to flash, you can do it without scripts or events. Use the A1 tileset and choose a tile the player can walk on (the poison swamp would be a good one). Place your floor tiles there, with one color/version covering the whole 6 tile 'group'. In the Tilesets tab on the database, make sure Damage Floor is turned off.
When you draw with that tile and play, it will animate between the tiles you've used to make up that autotile group.