I think it is more than reasonable for a shul to have a fair reason for having a rule requiring the baal tefila to wear a white shirt on Shabbos. I think it should almost be self-explanatory how a shul could have such rule that should strike everyone as being for a fair reason – even if they disagree with the rule.
You really think it would only be fair that BMG and Bobov and Brisk and Ponovoze should allow a guy in a colored shirt to daven for the amud on Shabbos?
Would you be upset with a shul rule precluding a man wearing green khaki pants with a black shirt from davening for the amud on Yom Kippur?