C# wpf mvvm programmatically change border color programmatically

I'm a beginner - I have a Border with an image inside, there could ultimately be many of these border/photos in xaml code.
The border(s) have an attribute Name="Border_N" (N = a unique border id value) I'd like to click on this photo which is a button and have the border change colour.
I want to be able do this programmatically but, I'm really not sure how best to go about this. I'm sure this can't be difficult, but I'm really not sure where to start. Anyone know?

You do not want to change your border color programmatically. You do not even want to change your border color when something is clicked. What you want to do instead is to introduce some state in your viewmodel, which represents the fact that "this photo" is clicked, (say, bool ThisPhotoIsClicked { get; set; }, hopefully you will find a more meaningful name,) and then you want to make your border select its color based on that state.

For this, you have a couple of options:

• You can bind the color of the border to the state using a binding with a boolean-to-color converter (see https://stackoverflow.com/a/32526689/773113)

• You can assign a style to your border which incorporates triggers to realize different colors based on different states (see https://stackoverflow.com/a/8534694/773113)