I need to add brake fluid to my recently purchased 97 SL 320. The current fluid is blue and not the normal clear/amber of DOT 3 or purple of DOT 5 ( silicone ). I've never had to use DOT 4 or 4+ before, is there a standard color?

Any idea if factory fluid is blue? I'd like to use the same stuff because the master cylinder reservoir is spotless inside and there is no sign that the master cyl / reservoir was ever replaced. Usually a black sludge will form after a few years using regular fluid.