Is there a way to make a layer invisible to the eyedropper?
I have a black and white bitmap as my top layer with blending mode of Multiply so the line art is always on top.
I then have various layers below for tracing the artwork in addition to drawing new objects. The issue comes in when I'm trying to use the eyedropper to copy/paste appearances between objects on the layers below. The top bitmap art layer Copy-blocks the eyedropper from the layers below that I'm really trying to copy/paste from. I'm always gettin a white (or black/gray) color with Multiply transparency when I use the eyedropper (from the bitmap art layer on top), when I really want to get the colors below it. Is there a solution for this?
Create proper transparency for the layer in Photoshop. The behavior is correct, you are mis-using the multiply blending mode.
There used to be a preference/option called 'Show Images in Outline mode' or something similar. Enable this option an set the layer to Outline mode (Ctrl+Click the layer's eyeball).