I'm pretty good at reading between the lines, but I have no idea what you are doing, so perhaps you'd provide some more details, and some screen shots. You can embed an image in a post by using the camera icon on the web page like this:
Please also tell us the OS and version, and the version and patch level of ID.
The transparency blend space will change the way blending works. If the blend space is CMYK and your black has some CMY in its mix you would get the tint you describe
Thanks a million! Things are so beautifully simple when one has the right answer!
Still much to learn on that topic of transparency space and so on I guess...
It works the same as Photoshop, the blend modes are really math calculations between the object colors, so the 4 color CMYK and 3 color RGB produce sometimes very different results. That's why in PS you get a warning when you try to switch color modes where there are blended layers.