Dear Rabbi. I heard that there is a spray that can be applied to cut pine trees (used for Christmas) that makes them last and look fresh longer. Could that be used ‘Lehavdil’ for the Schach of the Suka?

Haelef Lecha Shlomo (364) permits painting or spraying kosher Schach since it only changes the looks and the material remains the same. Halichos Shlomo (8: 8) is also lenient. However some Poskim are stringent if the color has a metallic look (gold or silver etc.) (See also Kovetz Halochos 5:1 and Piskei Teshuvos 629: 5).