Edit: Regarding the Event, daylight accounts into this. So take your shots when it's bright outside!!!
Will do that daily. More items in the description:
For Today: Red: Sunsettia, Snapdragon, Silkflower, Valberry, Chili
Also regarding blue and green:
Element Flowers give you ocher in the evening and while it rains
Matsutake or wheat does not seem to count for now.
Tried Crystal Ore, shells, Philanemo Mushrooms, Glaze Lilies as well, but so far no dice
Carrots trigger purple, not yellow or crimson.
But Cabbage does not trigger green or blue...