The 'Colours' palette window can be closed when the user detaches the window from its dock and selects the close button.
1. Run the latest Pencil v0.5 build for OSX.
2. Select the 'close button' along to top tool bar for the Colours Palette.
3. Observe the screen.
The Colours palette closes.
I expected that none of the subwindows will ever close or that a windows menu offers the user the ability to reopen them individually.
A current workaround for this is to select the 'Dock All Palettes' option in the 'Windows' menu.