It will be algae or lichen. Any proprietory soft top cleaner should kill it.Surely the green is algae and can be washed off?
The problem I found with any dye is that it goes on with a brush, or cloth, so you always go over a lot of it twice but not all. Then, of course, you will get darker and lighter 'patches'.I'm interested in recommendations as well. Treated mine with Renovo cleaner a few weeks ago (I've also used a Milton steriliser fluid mixture to good effect previously), and it looks a lot better, especially when wet.
When dry and in bright conditions it definitely looks like it would benefit from a dye process, especially at the leading edge where it meets the windscreen