Unknown 16 - First byte transparency

I found a map in Yuusha that had "46" for the first byte.

I took a simple water mesh and set the first byte to 46 and the water became transparent-ish and light!

Perhaps the 4 significant bits represent transparency level, while the other 4 bits represent effect.

We note that for an image with an alpha layer, 0C would not render the alpha layer properly. However if you chose 4C it would be correct.

I will be testing different values to see if there is any pattern. So far 06 an 46 both produce a light effect, but 06 is less transparent than 46.