Imagine if Apple asked users not to apply stickers to their laptop as it denies Apple the possibility to control their brand, or could make the laptop look broken, even unusable - shock I may even apply a sticker that shows a broken circuit board or simulates cracked aluminium. Apple's view is that applying a sticker to the case or keyboard render Appley documentation useless as they don't look like the pictures we screenshotted in moments.
> Even the slightest change in color can introduce friction between UI elements
Yeah, and? They might be the difference between unusable discomfort and usable, or allow ageing eyes to cope with arrogant and restricted developer choices, or missing sense of aesthetic. You might not like the colour car I buy or the decorating scheme I choose for my house. Mind your own damn business.
> On the topic of branding
Yeah, about that. It's branding that has led computer and phone makers to give highly limited theming capability. Firefox or my desktop is no longer my own to adjust and fiddle to unusability (sic) or perfection - as I see fit. Like the paint I use inside my house, mind your own damn business. I might LIKE my phone, Windows box and Linux box to all look highly distinct from each other for my own personal reasons. Mind your own damn business.
It is not another surface on which to stimulate my neurons to be further programmed by the brand. Baa.
Edit: Specifically on icons, I have been changing icons since the days of Workbench 1.3 in about 1986 or 87. I won't stop now. I've chosen wildly different icons for some apps at times - because they worked better for me. Icons as space for a logo is an entirely negative fashion to my mind as I prefer a hint, however vague, of what that a rarely used app does.