To set a shape opacity with Konva, we can set the opacity property when we instantiate the node, or we can use the opacity() method.
Shapes can have an opacity value between 0 and 1, where 0 is fully transparent, and 1 is fully opaque. Unless otherwise specified, all shapes are defaulted with an opacity value of 1.
If you want to apply transparency for several shapes without seen overlapping areas, take a look into Transparent Group Demo
Instructions: Mouseover the pentagon to change its opacity.