They're sad because they are white-coloured and undecorated.
Solution
Tiffi spreads sprinkles on their head and turn Golden brown.
Full list of appearances
Reality:
Marshmallow People are a minor character in Candy Crush Saga. They first appear in the 71st episode, Mellow Marshmallow. Before introducing level 1041, they have a new makeover by Tiffi, spreading sprinkles on their head.
Trivia
They are the first characters that appear as a group.
Due to April Fools 2020, almost all episode characters (but eight) have been absent from the game. A few other characters make occasional appearances in events.