Hi, not used blue but I have used black Renovo and it was a good product.
One bit of advice though, if the roof is old / original over the years of using you can get small areas that rub against each other and create smooth worn bits, when you colour treat these areas they can stick out as glossy compared to the matt finish of the rest of the roof, made my old 2.8 look awful. If you find any then Very very lightly rough these areas with a piece of medium sandpaper just to separate and lift the fibers a bit then the dye will adhere a little more uniformly. Also thoroughly clean the top before dyeing.