Use TemplateFill property to highlight selected item in Gallery – Canvas App

To highlight the selected item inside a gallery control, we can use its TemplateFill property. The default value is RGBA(0,0,0,0) Change it to If(ThisItem.IsSelected,RGBA(114, 189, 125, 1)) The result à Pick color from – https://rgbacolorpicker.com/ Hope it helps..