What setting causes Eclipse/RTC to provide syntax highlighting for a given file?
Using IBM's RTC, considering two .hpp files in the same directory, one has syntax highlighting and the other is black and white text. I can copy the contents of the "good" header file to the other and the "bad" file is still black and white.
Check the file text file encoding for both files (Edit > Encoding menu of an editor)
A difference of encoding might throw off Eclipse.
Make sure both files are opened with the same kind of editor view (like here for Java files).