So far it looks like possibly the white text was grabbing attention more than the other, but overall so far it looks like both could do a LOT better, and from the small version, I can see that neither really have the right contrast or brightness to really see what's going on, or maybe the shots you selected weren't compelling enough. 6.3 thousand people were shown that video based on impressions, but only 0.6 people have clicked so far, meaning you have a lot more potential for a click, but the thumbnail it'self isn't grabbing people attention and they're skipping right past.
You're allowed to mess with the original screenshot. I'd be boosting the saturation, contrast and brightness overall. You can make characters pop out more from the background by adding a colour wash or gradient over the background behind the character, by duplicating the screenshot, and cutting out the background, of the top layer, so the bottom layer shows, and then you can mess with colours in between the two layers. I find that helps a lot.
Interestingly 1.4% of those impressions are coming from recommended, which tells me your search impressions are probably very high, which is a good starting point. Your seo has seemingly done the job, it's brought the video to potential eyes, but the thumbs need work in generating enough interest to click. So I think if you try boosting the saturation and contrast and background colour, I think you have the potential to go from a 0.6 click through, to something more like at least a 2.0%
