Check the RGB values of the original shape.
1) Select the original shape, and click the "Fill" button at the top of the screen.
2) Click the custom color button (the little paint bucket next to the colored squares)
3) Click the "Define Custom Colors" button.
4) You will see your custom color selected. Make a note of the Red, Green and Blue values.
5) Close the windows so you are back at your design.
6) Select the new shape that you want to use this color on.
7) Click the custom color button
8) Click the "Define Custom Colors" button.
9) Enter in the Red, Greed and Blue values you noted before
This method also works for custom background colors.