Remember when IE didn't support it? And the goofy hacks Microsoft made people do to support transparency on websites?
You had to use Microsoft's DirectX filtering CSS extensions to properly handle the alpha channel of True Color PNGs.
Not exactly, palletised png supports a full alpha channel which did not work with IE.
Though you had to work to get that as usually software would limit palletised output to GIF (if you didn’t outright have to create your pngs from gifs).