The Schedule 1 By-Law that the Executive Committee’s (E/C) relying upon is #17 which states that “the Owner or Occupier of a lot must not, without the written consent of the Owners Corporation, maintain within the lot anything visible from outside the lot that, viewed from outside the lot, is not in keeping with the rest of the building”.
The intent of By-Law 17 (in 1996) was to manage situations such as where residents hung brightly coloured curtains or where Property Agents placed signage in windows, and the fact that it was omitted from the Model By-Laws contained in the 2010 Regulation is perhaps evidence of its limited relevance then and now, and particularly in your situation.
So whilst the bi-folds that you prefer may indeed be not “in keeping” with some of those windows in place elsewhere in the building, and even if By-Law 17 is relied upon it still permits a consent to be granted by the E/C on behalf of the Owners Corporation (O/C). The phrase “on behalf of” is important, because the E/C shouldn’t be expressing its opinion about what’s “in keeping” but rather those of the O/C, of which YOU are a member!
The overarching principle is that the E/C must behave reasonably in matters such as this and they’ll come unstuck if they don’t, but that said, the O/C does have an obligation to preserve, as far as is practicable, the “look” of the building as viewed from the outside.
Provided you also behave reasonably, and point out the matters that you’ve mentioned as your “defence”, and additionally that even though the windows are not technically “within the lot” (as curtains are) you’re willing to compromise, but that the E/C should also compromise on that as under the proposed Special By-Law you’ll be responsible for the maintenance of whatever windows are installed (that’s pretty standard unless the O/C wants to do that), so surely your preference must have some sway.