Revealing mistake: When Holden is driving his Ford explorer, the speedometer reads that he's going 0 mph. (00:50:35)
Continuity mistake: During the hockey fight, number 12's helmet is off, then on, then off again. (01:17:00)
Other mistake: Right after Cohee tells us the story of how Alyssa got the nickname "Finger Cuffs", after the shot returns to Banky and Holden, there's one frame with a significant 'burn mark' on the right side of the negative. Pronounced enough even to be noticeable at regular viewing speed. (01:10:30)
Continuity mistake: At the end, when the fan at the convention gives the last issue of Bluntman And Chronic to Banky to sign, Banky looks through the book with his pen in his left hand. It cuts away, and then back again, and the pen is in his right hand. (01:44:20)
Answer: I'm gonna be totally honest... I'm 99% sure there's no significance. In fact, I think it's just stained skin from all the smoking people do in the movie. Most people hold their cigarettes between their first two fingers. And most of the characters are depicted smoking throughout the film, which means they had to smoke a LOT during filming to maintain continuity. I used to get occasional orange (and sometimes yellow or light brown) stains on my fingers and hands when I smoked cigarettes. Especially if I smoked more than one in a short period of time and didn't wash me hands between them. So it's probably just smoking stains on the actor's fingers. In fact, I looked, and you see Banky holding a lit cigarette in his right hand and smoking during the story swapping scene you mentioned, with gives some direct evidence to my theory. (For reference, those stains can wash off with some good scrubbing).
TedStixon