Layer gray-ing out when another layer is added

Hello!  I have some scanned-in hand-drawn linework that is black with a transparent background.  I need to add a raster aerial image underneath the linework.  Whether I embed the aerial file, or place it as a linked file, or even just copy the image and paste it in as a new layer, the layer with the hand-drawn linework goes from black to kinda gray and transparent.  The linework looks fine if I turn off the aerial.  And then looks weird again if I turn the aerial back on.

I've used this same process to do dozens of rendered landscape plans in my career and never had this problem before.  Any ideas?

I need the linework to show up correctly (black) when the aerial is on underneath.  Thank you for your help!

This shows how weird the linework looks when I turn on the aerial:

This shows the linework looking correct when the aerial is turned off: