Hi Justin thanks for posting in the Community! Typically you could achieve this with a conditional formatting rule with your shape data (the event_name property) as your data source. You can read more about this in the conditional formatting article from our Help Centre.
However, it sounds like you are using custom shapes created from images of your UI rather than normal flowchart shapes in your diagram. If so- unfortunately this would not work as Lucidchart doesn't currently support conditional formatting for custom shapes. If this option would be useful to you, please promote the idea to our development team in our Product Feedback space.
There are ways you could work around this limitation. Say you want to visually highlight the nodes of the flowchart by creating a yellow border around them. I would recommend the following steps:
1. Drag a standard block shape onto your canvas and make it slightly larger than your node/screenshot.
2. Right-click and select 'Arrange>Send to back' then position it behind your screenshot so you can only see the borders of the shape. Make the shape transparent.
3. Copy the shape data from the screenshots to this block shape then use a conditional formatting rule with that shape data to fill the shape with a color depending on the shape data. (For example applying a yellow shape fill color if event_name=screen_1). This would have the effect of creating a yellow border outlining your screenshot when the condition is met.
I hope this helps! Feel free to let me know if you have any questions.