So..... RA is irrelevant when it comes to color?
For the most part, yes. The appeal of the RA concept is that it simplifies and otherwise rather complex subject to a great extent.
Then what are the variables you use to draw the correlation between the water used in a brew and the particular brew style? If I'm to forget about RA / Style SRM what do I replace it with?
You need to understand not only what the water of Dortmund is like but how the brewers there treated it. Being that it is in Germany it is very likely that it was decarbonated by boiling or lime treatment and then acidified by sauergut (or the mash was). For Export you want that crisp mineral quality. You have to understand how to get that. One approach would be to use RO water with calcium chloride but no alkalinity at all. That will control mash pH. You can fiddle with the calcium chloride addition until you optimize the taste of the beer. You can even do this after the beer is brewed and in your glass i.e you can add calcium chloride to finished beer and use the tasting results to guide you for successive brews. Please understand that I have never brewed and Export and am therefore speaking only in very general terms.
The point is that you can't take the easy way out and hang your hat on RA alone. You must research the style. Ray Daniels "Designing Great Beers" (or something close to that may give you ideas. I don't think there is one for Export but the AHA has monographs on many other styles.
I need to take another look at Bru'n water...
That's probably a good idea.
Getting back to the original topic, Are the explanations I hear that Pilsen water makes a good pils and Dublin water makes a good stout compete BS?
No, not at all. In the case of Pilsen the very low mineral content is a major characteristic of the style. But you can make a better Pilsner (IMO and opinion does count a great deal when talking about something like beer quality) by increasing the chloride to just below the point where the associated cation(s) begin to be noticeable (beer starts to taste minerally).
Burton ales require a lot of sulfate to give them the authentic hops punch that one expects of such beers. But again you can make a better beer by holding back on the sulfate.
With stout you have lots of flexibility as the roasty flavors are the dominant ones even though you can have them sweet, dry, hoppy, smooth...
As it might help, here's the thought process that goes into designing a stout:
1 How roasty do I want it to be. That determines how much roast barley
2 How dry do I want it to be. That determines what sacharification temperature to use, whether lactose will be added or not.
3 Will it be too thin? Dry stouts can be pretty watery and so either lactose is added or flaked barley
4 How hoppy do I want it to be and how do I want the hops character? That determines cultivar and wheter sulfate is to be allowed or not.
5 How big a stout do I want? That determines the base malt amount (with roast barley, flaked barley and any other additions being percentages of that).
My feeling is that the color will come out to be whatever it comes out to be. There isn't much difference (except to a spectrophotometer) between a 40 SRM stout and a 140 SRM stout.