The effect I was trying to achieve was partly a few hyperlinks and partly the look of some editors which display keywords and other significant tokens in different colours. This looked like a good java program to write so here it is. I've just added the features I was after and the program is far from complete. Here is a list of the features it has at present. Takes a .asm or .h file and outputs a .asm.html or .h.html file.
Listing is displayed in a fixed font.
Comments are displayed in green . Lines beginning with directives are shown in red . Included files are shown as hyperlinks. Labels referred to in gotos and calls are shown as hyperlinks. Clicking on labels which are not external to the file will take you to the label.