You use a zipper to close this bag. Maybe not a good choice if you prefer lots of colour choices, but it does come in purple and it has a volume of 30 litres.
From Amazon
Fjallraven 23802-457 Kånken Weekender Sports backpack Unisex Pastel Lavender Size OneSize
Scandinavian Outdoor Store
Fjällräven Kånken Weekender