Adds an event handler that runs when an element's color value is changed.
An element triggers a change event when a site visitor changes the color value in the panel element.
A change event is not triggered when you change an element's color value using
the element's color property in code.
Because onColorChange() is fired before validations are performed, do not check
any of the validation properties in the onColorChange() event handler. For example,
do not code an if statement that checks the valid property in onColorChange()
because the property at this point contains values prior to the onColorChange() event.
handler(event: Event): void The name of the function or
the function expression to run when the element's value changes.