After enabling scripting in the editor features and opening the global page script, enter this:
$PAGETEXT := "<style></style>" + $PAGETEXT
That's the basis for restyling, and all the code (CSS) for recoloring goes in between <style> and </style>. You mentioned changing text color to white, as well as, in another thread, changing link color. Here's the code you'd use to make page text white and links red, for instance:
p {color: white;} a, a:hover {color: red;}
So, all together, you'd use:
$PAGETEXT := "<style>p {color: white;} a, a:hover {color: red;}</style>" + $PAGETEXT
