Welcome to the Decker community, Specterette!
Exploring dead online forums is a fun idea. Gray Lo-Fi's Old Web Cobwebs might be a useful source of inspiration!
Text in Field widgets is generally either black-on-white (default) or white-on-black (If the widget has been set to "Show Inverted"); at present you can't simply change the color of some text, but depending on your needs there are several options that might do what you want:
If you set a field widget to "Show Transparent", you can draw in color underneath it, but the "foreground" text will be black.
If a field doesn't need to be interactive and you just want visible text, you can select a widget containing text, choose "Edit -> Copy Image" from the menu and obtain a "screenshot" of the widget which you can paste elsewhere and then manipulate with normal drawing tools. (This works for any widget!)
It is possible to customize Decker's 16-color palette and remap black/white to some other color. Harlequin Diver's Fear and Loneliness in Latona's Void is a good example of how this aesthetic turns out. Scripts can modify Decker's palette on the fly, so it's also possible to give each card a distinct palette with some extra work.
Rich-text fields can contain inline images, which can use any colors, but this feature isn't generally ideal for text input.
It's also possible to draw text- or anything else- in color on a Canvas widget with scripts. In principle it would be possible to build a Contraption offering a more colorful text widget depending on what exactly you needed to do.
Does any of that help?