Coloured ASCII-work in HTML by Allen Mullen. His oldest dated work is from 1994, but he was probably active long before that. His great archive of Usenet ASCII goes back to 1991. He stopped working with ASCII around 1996.
He called this gifscii, because it involved converting GIFs to ASCII. He also called it pictures rather than art, to avoid discussions and insults about the merit of his work.
Mullen often drew the images from scratch with a Wacom tablet. He used three shades of grey which the gifscii converter turned into $, M and !. With a word processor’s replace function he’d introduce areas of C and :. He used macros to even out the edges and did a lot of manual editing. “I don’t believe it would be practical to try to copy my methods. There’s a lot more to it than I can describe here.”
Colour could be added in browsers such as Netscape Gold by selecting the text and choosing a colour. Most browsers supported a palette of 256 colours. Of course, colour could also be added manually in the HTML code.