There will always be exceptions to the rule. Heavy token users dont care as they heal immediately and just buy more.
On my level 4 account, I have one injury (6 days) and 19 reds.
On my level 3 account, I had 51 reds and SEVEN injuries over the past 3 days. I dont play friendlies at all.
I dont waste my tokens on any colour packs.
I dont like friendlies at all. I think there is more chance for injury than just training, but only Nordeus knows.