I am trying to copy and paste from one FrameMaker file to another, but when I do, the resulting text is blue (it's black in the source document). When I try to apply a style to it, it remains blue.
Any ideas on what is causing this to happen?
Sounds like you didn't do a paste-special-unformatted, and the copied-in text brought one or more styles/formats, color definitions, or even conditions, in with it.
What do the character and paragraph designers show for color of the text? If they show black or As-Is, I'd check to see if a condition was applied with the condition indicator set to ON.
Check that track changes is not activated as well.