MS Word: Object background always gray

[Peachman]

Since last evening, in MS Word, the background of every object that ought to have the same
background as the document (after setting the background color to "no filling") is gray. When
I try to set it for example red and 50% transparency, I don't get a color between red and white
but between red and gray. However, when I open the printing preview or actually print the
document, the colors are as they should be.
Why is that and how can I change it?

[soybean]

I gather this is not a mere text document.  Can you tell us more about what you're doing with Word?  What kind of "object" are you inserting? 

[Peachman]

It's the same with all objects whose background should be transparent, for example
excel diagrams; in my case it's structural formulas from a chemistry program called
ChemSketch.