Blocks that are only passable if the color Switches have been pushed. The graphics of the blocks don't change though.
These blocks can be recreated by Switch Pack if you set the flag to any of the switch flags (which are mentioned in a comment inside the blocks).
Furthermore, more accurate inverted !-blocks (which doesn't require ExAnimations, for example) can be inserted with ObjecTool (even if it's more difficult to insert than one with GPS). A basic object:
LDA #$6A ; $6A for green, $6B for yellow, $6C for blue, $6D for red
LDA $1F27|!addr ; $1F27 for green, $1F28 for yellow, $1F29 for blue, $1F2A for red