Once you have finished your watch part it is time to consider some of the post effects users can apply. Especially with watch hands, users can change their radius (length) and thickness afterwards. To make this work as intended you have to think about the scaling properties of your shape.
To make you shapes scale nicely (thickness and lenght), some shapes might require different methods than others. For instance when you have circles in your watch part you probably want them to remain circles even if the scaling in X direction (thickness) and Y direction (lenght/radius) is not the same. This is handled by setting the correct scaling properties for your shapes.
You can access the scaling properties from the overflow menu on the shape layers (button 7).
Keep in mind that the colors of your watch part can easily be changed afterwards, outside of the watch part designer.
Changing the palette of a watch part is done by tapping the multi-colored round button in front of the chosen watch part in the main interface of Pujie Black
This will show the following dialog, which will allow you to change all the colors in the watch part.