The Draw | Image | Colors | Select
Transparent command 
allows you to select up to 256 colors to specify as
transparent on an image. If an image with transparent color is overlayed
on top of another object, the object beneath the image shows through.
Transparency can be slow. Use as few transparent colors as possible if
the program is running slowly.
View selected colors in the Select Transparent Color dialog
To create transparent colors:
1. Import an image.
2. Select the image.
3. Click Draw | Image | Colors | Select Transparent.
4. The
cursor turns into a crosshair 
. Click on a
color in the image. This color is entered into the Select
Transparent Color dialog.
5. After all the colors are selected, click the OK button to create transparent colors.
See Also