Adobe AFTER EFFECTS CS3 PROFESSIONAL User Manual page 266

Control mask path color
To help you identify and work with masks, the Composition and Layer panels outline a mask's path with color, and
the Timeline panel displays that same color next to the mask's name. By default, After Effects uses the color yellow
for all masks. To make each mask more distinctive, you can manually change a mask's color using the Timeline panel,
or you can set After Effects to cycle through mask colors for new masks.
Apply a new color to a mask outline
To make it easier to work with multiple masks in the Composition panel, you can apply different colors to each mask
outline.
1 Select the mask in the Timeline panel.
Click the color swatch to the left of the mask name, pick a new color, and click OK.
2
Set After Effects to cycle through mask colors
Choose Edit > Preferences > User Interface Colors.
1
2 Select Cycle Mask Colors.
After Effects cycles through different mask colors.
Mask modes
Blending modes for masks (mask modes) control how masks within a layer interact with one another. By default, all
masks are set to Add, which combines the transparency values of any masks that overlap on the same layer. You can
apply a mode to each mask, but you can't animate a mask's mode—that is, you can't change a mask mode over time.
You choose a mask mode for a mask from the menu next to the mask name in the Timeline panel.
The first mask that you create interacts with the layer's alpha channel. If that channel doesn't define the entire image
as opaque, then the mask interacts with the layer frame. Each additional mask you create interacts with masks located
above it in the stacking order in the Timeline panel. The results of mask modes vary depending on the modes set for
the masks higher up in the stacking order. Mask modes only operate between masks on the same layer.
Using mask modes, you can create complex compound masks with multiple transparent areas. For example, you can
set a mask mode that combines two masks and sets the opaque area to the areas where the two masks intersect.
AFTER EFFECTS CS3 260
User Guide