[fedorareis]

Why does the folder color matter? Is it just because that is what you are used to from a specific OS?

Color helps for some people but when making an accessible design you have to account for color blindness and other vision issues. Which means the icon needs enough contrast and can’t rely on just color to convey meaning, unless the icon is paired with a text label that also conveys the meaning the color was trying to convey.

So while I agree that color iconography can be extremely helpful for the average user, unless it is supplemented by other techniques it can make a product completely unusable for a subset of users

[fmbb]

The commenter did not say yellow was important per se, or that the color yellow was the most important property of the icon.

The commenter said that adding distinct colors to icons help users tell them apart.

[mlx0x]

Folders were always yellow on Windows because people were used to Manilla folders.

[layer8]

In the example, the folder is recognizable as such from just its shape. The color merely makes it more recognizable (because folders are yellow on Windows — it reinforces that the icon depicts a file folder).

For accessibility reasons, you shouldn’t rely on only the color, but that doesn’t mean that color isn’t a very useful property to apply.