Whilst inputting notes one them turned pink.
Why is this? I tried searching but found no results. 
Thanks.
Like this?
That indicates a note that’s out of range for the instrument. There’s a deeper red for notes that are difficult, but possible. (Or possibly it’s the other way round.)
They won’t show up in printing, but you can turn them off on the screen in the View menu > Note & Rest Colors.
Thanks Benwiggy, that was it.
Strange though because it’s a mandolin part and the note is within range for the instrument. No matter it’s hidden now anyway.
For fretted instruments, pink notes denote notes in range, but currently unplayable due to the chord voicing. For example, a low G and middle C cannot be played on a mandolin simultaneously because they both need to be played on a the G-string.
Thanks Chuck.
On taking a closer look I found that exactly was it. I had inadvertently place a ‘D’ note on the open ‘A’ as a chord which, of course, isn’t possible for a standard tuned mandolin.
Isn’t Dorico clever? 