It's not the art itself, but a difference in how the new client draws. From what I understand- the old client used destination color matrix, and the new one only uses source. Basically that top layer piece of art can't affect the layer behind it to give the same translucent effect.

I don't know enough about the draw code to tell if this is a simple, or complicated thing to change. Then there is the question of priority versus fixing something else.

FWIW, this affects (or is it effects? )  Nature Shield, Soul Blade, Aegis, maybe some others. Here is a side by side of how they used to look vs now: