Red notes on F horn

Upon inputting a high F into the F horn stave (a Bb in concert pitch) the note turned a fairly dark shade of red, presumably indicating that it was outside of the comfortable range for a horn player as is stated in the handbook. However, as a horn player myself, and not a particularly good one at that, I can testify that this is well within the range of a horn provided that nothing too complex in terms of rhythm is required. Is there any other reason for this occurrence? If not, then I would recommend the range of the F Horn being changed so that up to a top Bb (an Eb in concert pitch) is acceptable as that is what the ABRSM grade 8 range requires.