I don’t think there is a simple way to smoothly change sliders and have it update right now, outside of Dynamo…
You could make a custom family template with the green, brown and reindeer materials, then generate the family in player and hit ok… That bakes it into the revit file and updates it, but given that Player doesn’t keep element binding, you will get a new tree each time… perhaps you would have an ‘offset’ parameter…
You could theoretically have a Form which shows the Image, and a Form with a Trackbar? When the number is updated you kill the image form and generate a new one with the new image? You would need to intercept the ‘change’ as your trigger?