What are the competing formulas for determining target Residual Alkalinity from SRM?

This article will probably shed some light on the subject for you (it did for me). Also, see this article for a more specific discussion on the correlation of color to pH.

Remember, though, that the relationship between color and pH can be quite loose. The final remarks in the first linked article state "the approach outlined here only provides for a crude estimation of the mash pH and that there are cases where this prediction will not be correct". To quote Palmer, "You can use the calculated color of a beer recipe as a guide, but don’t rely on it as gospel to determine the appropriate amount of residual alkalinty; it is a general relationship, like cloud color and rain".

Hope this is helpful.

e: Worth noting that the experiments on which these conclusions are based note that "[i]t was found that Kolbach's pH change based on residual alkalinity is generally used incorrectly in (home) brewing and that it depends on more factors than just the residual alkalinity of the brewing water when mash pH is of interest" (the Kolbach method being cited by both the Palmer and BYO articles).