Collecting colourful leafs, putting them between two sheets of plastic foil and the blinds are done. They stick to the window without any sticker or tape.
My leafs were slightly weat so it appeared some unexpected frost effect.
Only one more idea at the end: you should better first herbarize the leafs like those in my frame so they don’t dry or lose colour. Leafs from this year could be used the next. This was my experience this Autumn.