About the Onion Skin
With onion skinning, you can display the previous and next drawings and refer to them to determine the size, angle or position of the drawing in the current panel.
You can display the drawings from previous panels in the current panel, so you can see where to place the drawings for the next panel.
You can also display drawings from the next panels in the current panel, so you can see where to place the drawings for the previous panel.
By default, previous drawings appear in a shade of red and next drawings are displayed in green. You can change the display colours of onion skinned drawings in the Preferences dialog box (Colours tab).