Last year, I had a glorious week on Mull in early October. The leaves were beginning to change. I could see the different types of weather being received by other parts of the island and on the mainland across the sea. Only one day of drizzle while I was there, but the trip back to England was very wet. The rain started at the ferry terminal and just got worse and worse until I crossed back across the border. Absolutely torrential across the high section of the motorway south of Glasgow. But the following morning was glorious in Cumbria.
All very much luck of the draw. There are many micro-climates in Scotland, so it's difficult to say what you're going to get each day - you may even get all of them of the same day! I was in Edinburgh in February and we had rain, wind, sunshine and snow, all in the one day.