> One of the basic rules of thumb in typography is that, when writing a piece of text, you should choose one typeface and stick to it. Likewise, a splash of colour may grab the reader's attention, but it will inevitably decrease the legibility of the text. The natural flow of the text is broken, and it takes more brain effort to piece together the individual letters into words and semantics. Cognitively, the reading process becomes slightly less automatic and slightly more conscious; leaving less room in the conscious part of the mind for actually understanding the text.

https://www.linusakesson.net/programming/syntaxhighlighting/