Leave it to the Swedes-Fjallraven Kanken

I am contemplating walking to work on the days that I do not want to cycle. I desperately am looking for a nice looking backpack (or rucksack) to carry my things in so I don't get that hunched one shoulder pain.  I found a cute topshop one but for some reason this little leather version would look better worn as a one shoulder backpack Wang look.
My friend came into work with her gym bag and it was by the iconic Swedish brand Fjallraven, named Kanken circa 1974. I instantly saw this as a well crafted, cool and timeless bag that can carry your camping gear for festivals and your gym gear for, well the gym. I am planning a trip to Stockholm this summer so I am sure to pick one of these up, but there are soo many colours to choose from! What colour do you think I should buy?