color

Color notes outside the usable pitch range
https://musescore.org/en/handbook-advanced-topics/preferences#note-input
;-)

and https://musescore.org/en/handbook-advanced-topics/staff-properties , usable pitch range

Impossible to tell from just a picture, but presumably you told MuseScorer to write music for some instrument other than flute. Those notes are well within range for a flute, but might not be for, say, a cello, or bassoon. Probably you originally selected some other instrument. If you post the actual score rather than a picture we can say better.