A color coded legend.
A Legend widget contains color and labels. The items in the legend can be selected and an action performed. Legends are used to easily change between discrete values with associated colors.
For example, when defining the type of joint among three options (Active, Locked, Free).
List of values which are not deactivated (shown as transparent).
Pass True to activate or False to deactivate all.
List of (color, value, label) tuples populating the legend.