The Color Key Effect

Color Key is one of those effects that can be a bit difficult to see an immediate use for. Effects like Glow, Edge Fade, Transparency and so on are very clear already from the name, and it is easy to think of scenarios where those effects would be useful. But what of the Color Key, what can we really use it for? When does it make sense to use it? It’s not quite as clear.

I didn’t really use this effect myself in the beginning, but I’ve been using it more and more over the years as I have found that it can really simplify the work process to get the look I need.

The main idea behind Color Key is that it can be used to remove parts of a sheet, allowing the sheet below to shine through. This can be done to punch hole in things, for example, you can use it to punch a hole in the landmass to see the sea fill below (creating a lake), you can punch a hole in the roof or wall of a building to see the interior, you can use it to remove the parts of the grid you don’t want and so on. But instead of actually deleting anything from the map, the Color Key is just an effect that can be later moved or removed, for example making it much easier to reshape that hole in the wall as opposed to if you had actually edited the wall entity itself.

What the Color Key effect does is to look for pixels of the specified color in the image, and then turn these transparent so you can see what is below. So to use the color key effect, the normal procedure is to draw a polygon with a solid color on a sheet, and then set up the Color Key effect to target that color. Let us start by a simple example of creating a lake.

I’ve started here with a tiny map in the Mike Schley overland style depicting a small island. You can download my map. All the images in this article are clickable to see a larger version.

I then make sure that I’ve set my current color to color 6 (pink), the Fill Style to Solid, line width to 0 and my sheet to LAND (The same sheet my landmass is on).

Now, I just use the basic Smooth Poly tool to draw a lake-shaped poly on top of my landmass.

The final step is to add the Color Key effect to my LAND sheet. You’ll normally want to move the effect up in the list so it is the first effect on the sheet, and not the last.

Closing the dialog should yield us this.

Notice how the glow effects from the sheet also applies to the edge of our new lake. This happened because we put the Color Key effect at the top of the effect list, causing the “hole” in the landmass to be created first, and then when the glows are subsequently applied they would see the edge of our lake as well as the outer edge of the landmass. If we had placed Color Key as the last effect in list instead, then the glows would have been applied at the edges first, and then the hole would have been made resulting in no glows around that inner edge.

What we have done here is similar to using multipoly to make the landmass a shape with a hole in it, but the advantage here is that we don’t have to modify the landmass at all to achieve this. While multipolies are fine, they are a bit more cumbersome if you need to change things later. Not so with Color Key, since the “lake” poly is completely independent of the main landmass poly.

As you can see, the effect is really easy to apply, but let us mention a few reasons why it might not work as intended and things to watch out for:

  1. The Color: The entity we drew needs to have the same color as the one defined in the effect. The default color in the dialog when adding the effect matches color 6 from CC3+’s color palette. You can use any color obviously, but it is vital that these are 100% the same, “looking similar” doesn’t cut it. You can click the big color swatch in the dialog to pick from CC3+’s palette, or you can specify a color using RGB values. Notice that this exact color match is also one of the reasons why we place this effect as the first one on the sheet. Many other effects might modify the color on the sheet, so the polygon might for example have been darkened by another effect before the Color Key effect happened, and as such, the resulting color doesn’t match any more.
  2. The Sheet: The polygon used for the Color Key effect must live on the same sheet it is going to punch a hole in, you can’t put it on a separate sheet.
  3. What’s below? The effect punches a hole in the sheet, giving a view to what’s below. But it won’t magically put anything there. If you punch a hole in the roof of a house, you’ll obviously have to draw the inside of the house yourself on a lower sheet. Note that you can use this effect on multiple sheets in succession to punch a “deeper” hole all the way through, for example through both the terrain and the landmass to see the sea below.
  4. On Top: The color key poly needs to be the topmost entity on the sheet. You will only get holes punched where the poly is visible. You can’t hide it below the floor and still expect a hole to be punched in the floor. It is the visibility of the color that is important, not the existence of the poly.


Punching holes in landmasses to make a lake is just one of the possibilities when using this effect. Let me show other uses of this excellent effect.


In my blog entry about perspective ruins, I used the color key to help me create a ruined wall. Perspective entities can be a bit tricky and lots of work to modify, so even if I did need to do some additional manual work in addition to using the color key, it really made the process of making a ruined wall much easier


That blog entry was actually based on a map, Araneae Keep, which I did for Christina Trani’s mapping contest, where I designed a ruined keep in perspectives. For the same map, I also used the color key effect to knock out part of the roof. The top of the keep was drawn using the regular house tool in Perspectives, which comes with both a wall and a roof, and then I used the color key to knock a hole in the walls and roof. Of course, CC3+ isn’t a 3D-modelling program, so doing this doesn’t really let me see inside the house, but I can then work on the sheet below the house and place things there and create the illusion that we are looking into the house. But in reality, the entire house is on the same sheet, so what I am really doing is seeing through the entire house.


And finally, I used it in my recent map for the Community Atlas 500th map competition. I used it for several purposes here, but one of the most important uses is to cut a chasm-shaped hole in the center room, as well as in the grid. The center room is really a whole hexagon-shaped room here, but I made a copy of the chasm polygon, changed the fill to a solid pink and placed it on the same sheets as the floor and the walls of the room to cut out the shape. I also put a copy on the grid sheet to remove the grid above the chasm.


Hope this helped you find some inspiration for how to use this effect. A few other inspirations may be Joe Slayton’s Effectia and Gerri Broman’s Forrestal Chapel. If you watch my livestream recording about Perspective Cities you’ll also see that I use the effect starting at about 10 minutes into the video.


If you have questions regarding the content of this article, please use the ProFantasy forums. It can take a long time before comments on the blog gets noticed, especially for older articles. The forums on the other hand, I frequent daily.

One Response to “The Color Key Effect”

  1. One of my favorite sheet effects.

    One thing I do to make it even more useful is to create a separate layer (I usually call it COLOR KEY 6) and when I draw my colored polygons I always put them on that layer so I can quickly hide all the color key effects in case I want to work on the map with sheet effects off but not see all that bright pink all over the place.