Certainly read your By-Laws. Potentially useful no matter what.
If your By-Laws specify only a colour for the outward facing surface of a window treatment then you could go ahead with your blinds confident in the knowledge that you are doing the right thing, no matter what your neighbour’s interpretation of the by-laws might be.
If your by-laws are ridiculously specific and narrow you might get involved to have them changed. For example, you should not be obliged to get (say) a particular style of white venetian blinds that might not even be available any more because the by-law was written before you could get (say) white cellular blinds that would provide both insulation and privacy.
I do think consistent appearance can matter in some designs but what matters and what does not is very particular to the specific development/building.
In the ACT “an amendment to the rules of an owners corporation (ACT-speak for By-Laws) has no effect to the extent that it results in the rules … prohibiting or restricting the installation, operation or maintenance of sustainability or utility infrastructure.”
I mention that last point so that people interested to lobby for improved strata legislation elsewhere will know what is possible.
So, in the ACT, a rule specifying a consistent colour (say white) for window treatments would be OK and might be important for the aesthetics of the property, but a rule that prevented a unit owner from installing heavy, close-fitting curtains or cellular blinds that would provide better insulation would not be OK.