[delinka]

"...a splash of colour may grab the reader's attention, but it will inevitably decrease the legibility of the text."

This depends entirely on the content of the text. Stories, fiction, non-fiction, reference material ... information where one human is intending to communicate with another human should limit use of color.

For source code, that humans do read but is intended to be parsed and compiled by a computer, I'm not assembling (in my head) the whimsical trials of a protagonist - I need to see structure; color gives me a quicker overview of the structure of a line, function, class, etc.