The first Thumbnail is vibrant, and clearly depicts the video contents, it is also pleasent and "pretty". It had a CTR of 5.2%.... The Second Thumbnail barely paletable, not nearby as "Pretty". But it has a CTR of 12.2%. Focus on clickability over aesthetics for your thumbnails

The second video I released on my second channel flopped, hard... Until I changed the thumbnail, and it skyrocketed in views and built the foundation of the entire channel. From Sixty views a day to over a thousand daily average views. Now, two years later this video has made a total of 900$ and still averages one thousand views a day. All by simply improving the clickability of the video. Taking the CTR from 5.5% to 12.2%