(It both is and isn't, depending on the use case, but I'm pretty sure nobody's design needs to make a difference between #123456 and #123457.)

Except for a tetrachromat. Specifically, a strong tetrachromat that has both four colour channels in the brain and a different frequency on the fourth cone.

Who are, admittedly, hella rare. Apparently there are less than a few dozen confirmed world-wide.

But they do exist.

Do CSS minifier really adjust the colors in the CSS files to get better compression rates or to reduce the number of rules in the CSS?

https://news.ycombinator.com/item?id=47390945

What is a NASA number?

Allegedly, within NASA, there is only a need for so many decimal places. If I can remember correctly, nine digits would get a spacecraft to land within a metre on the rock formerly known as the planet Pluto. So no need for that, unless you are going to 'occupy Pluto', building a few AI datacentres there.

In the context of SVG, usually it is icons that I encounter, where the artworker has exported something like a search icon, which is a circle and a line. These can be specified in SVG using integers, and single digit integers, if you really want, but let's make it two digits.

However, does the SVG file from the artworker have a viewbox containing a circle and a line? Nope. Instead you get one circle for the outer part of the circle in black and another smaller circle in white. Oh, and a line. The circles will be written as polygons with about two hundred vertices, with all vertices specified with NASA numbers (as I call them), typically six decimal places.

As a consequence, the file, which should be six lines of human readable code balloons to many kilobytes of nonsense. Yes, this can be put through SVGO but that will just remove some decimal places and make the file even less human readable.

As a developer, the simple file is great as the inevitable adjustments can be applied easily, maybe to make the icon bold or to adjust alignment within the viewbox. However, when given artworker files with NASA numbers, I then have to raise a ticket so that I can get the corrected file two weeks later from the guy sat in front of a massive Apple monitor with headphones welded on.

The reason for not using NASA numbers has nothing to do with bloat, as no optimisation will make up for the mountain of javascript the marketing guys have bundled into their Google Tag Manager, it has everything to do with efficient workflows.

Generally the customer does not care about fonts, colours and much else that designers fret over. If we went back to the 216 'web safe' colours of yesteryear (for CSS, not images), would anyone notice? If we could not load custom fonts, would most people notice? They might, but this would not prevent them from surfing the web.