I got it. They simply don't look good. It looks cluttered to me.
We already have two indicators that a transaction was incoming or outcoming. This is "+ /- " before a value, and the title "Sent ETH" or "Received ETH".
We can think of a gentle way to flag it. How about the one in the middle? What do you think?
Also, let's not forget that red–green color blindness affects up to 8% of males.