Checked out the "Disable colouring in messages" checkbox in the custom theme editor (found in User Preferences near the top of the right hand column), and it does what it says. It does not do anything to the tags that cause text to be displayed in color, it just
ignores them site-wide.
SillySnowFox:
So the question is this, anyone know the settings to either make a custom skin that's identical to the 'black' one just without post colors or how to remove the post colors using something like GreaseMonkey?
To answer the original question: go ahead and set a theme you want your custom theme to resemble, edit that theme to get your custom theme set up with the colors and effects you want it, click the checkbox for "Disable colouring in messages", then save your new custom theme. Done.