ColorKey doesn't cut through terrains

I'm making a map and had a large block of terrain fill. I wanted to cut holes to see the landmass underneath, but it didn't work.
I had ColorKey at the top of the list of effects for that sheet - so how come it sank to the Landmass?
PS it sank to the Common Sheet!!!!!!!
Comments
Are your pink polygons on the same sheet as the terrain you want to cut through? For it to work, there are basically 3 conditions
It is easier to see what you might have done wrong if you post your .fcw file.
I'm sorry but that file has been overwritten but the top two were right. I didn't realise I had to match the cutting polys - I thought the magenta was the only colour for ColorKeys; every video I've seen has been the magenta. I hadn't realised that effects had to be on either.
The Color Key effect can work with any color you want. Magenta (Color #6 in the CC3+ palette) is used by default since very few maps would contain this color naturally, but it can be changed to another color if you need to.