I found a great answer to this from user "Bond" here:
but it doesn't completely work.
As described in the answer linked above, I edited my VB6.EXE, changed some of the colour values in the colour palette, and was then able to run VB6 and choose the modified colours (Tools->Options->Editor Format) for text items in the editor.
The problem is, the settings only last for as long as VB6 is running. When I restart VB6 the items that once had a custom colour are changed to some other colour in the list. The modified colours still show in the list, but they are no longer associated with any of the text items.
For example: just now I tried changing several items to one of the modified colours. When I restarted VB6, most of those items were changed to white, and the rest to 'Auto'.
Has anyone been able to make this work properly? Does anyone know what's going on?
EDIT: The problem has to do with the colour values saved in the registry. I posted more information here: http://superuser.com/a/573874/201334. Still looking for a solution.