The 1.4's have some colors and the 2.0's have others. Its very confusing, and Kenko does not even admit to it.
I can say that the red dot 1.4X is very old (two red dots actually, one is to line up the TC to mount it. Very strange. It locks up newer cameras. I also had the blue dot version when it came out. It works with a 5D MK III on many lenses, but locks up with others.
At the time (2012), the 2.0X had a green dot.
The bottom has dropped out of the price for the 1.4X, it has issues on almost every Canon DSLR releasedin the last 3 years.
If you have a 5 year old camera, its fine.
I don't know if Kenko has ever fixed the issue, they do not return e-mails asking.