Renders sort of "see through"

anaximanes_2000

I have been working on my D:BB redux, since I am putting Desideratum onto Steam, and I have noticed that there are, in some shades or shadows, a "see through" effect in the renders.  That is, say I take it into photoshop, I can see the "blank layer" checker pattern through it.  I am not sure why it is happening, unless it always does, and I never noticed until now.  There is no "opacity" settings on- in other words- everything is at 100% opacity.  Will show you a screenshot.  In it, the red latex is an example of this where you can see that it is slightly see through- NOT in the scene itself- but in the output.  Any idea why?