does no respond to color change
A Notifier must be invoked by an event handler of some type. You are not getting a response to a color change somewhere in your code. You do not share the Blocks you are trying to use so only can guess.
A guess is you probably want to display an ShowAlert( notice ) that will display a temporary notification. Here is an example using a Button event handler. Perhaps some code like this:
What you do to use a Notifier to alert you to that color change depends on what in your app is changing color the color property of and the control you use to determine the change.
Share more information and someone will probably provide specific advice.