Why do Photoshop and Krita use grayscale icons? [on hold]

The toolbox in both applications use icons that have no colors. What's the reasoning behind this? What are the pros and cons? I've heard that some people can get overwhelmed by colors... is that it?

Here's Krita:

enter image description here

And here's Photoshop:

enter image description here (Source: https://photoshoptrainingchannel.com/wp-content/uploads/2015/12/customize-toolbar-photoshop.jpg )

By comparison, here's paint.net:

enter image description here

Personally I find this much nicer - prettier to look at and I can more easily find an icon.

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