FT4 and FT8 are normally on different frequencies from each other. If you don't have WSJTX set up to control your radio, then that is probably why your display is turning red.
Sent: Thursday, February 13, 2020 5:49 PM
To: WSJT Group
Subject: [WSJTX] FT4 vs FT8
Is FT4 used in the same band as FT8, because if I change to FT4 from FT8 the frequency display turns red, why is this happing.