to a photograph that appeared in The Illustrated London News on this day, 107 years ago. King George V had been king for just eight days and is pictured in naval uniform along with the future Edward VIII. Queen Mary was resplendent in an Edwardian feather trimmed hat.
Embed from Getty Images
Photo from Getty as indicated
Royal Hats 
If the photo is eight days after the accession then mourning would have been over but if it is eight days after Edward’s death then yes then surely Mary would have been wearing black. No matter the hat is stunning. Mary wore the Edwardian style well!
The photo was published May 14, 1910 but I suspect it was taken earlier.
Yes, and there are no black armbands on the men.
Accession is instant upon the death of the preceding monarch, if I am not mistaken, so I don’t think your distinction between them holds. There are, or were, several types of mourning of different lengths, dependent on whether one was a member of the royal family or their households, of the public, of the court, or in the military service. These were not always the same length from reign to reign, but it would be very likely that the queen would still be in black if the photo had been taken, as opposed to published, on the day Getty indicated.
Above is @Michell’s point.
Would it be just a few days after the Coronation, not the accession? I also noticed she is not in mourning.
Exactly what I thought!
I wonder if Getty’s dating of this photo is accurate–if George V had just succeeded to the throne, surely the queen would have been wearing mourning for Edward VII?