As graphics hardware does not typically care what kind of monitor is connected, the software would have no way of knowing if a monochrome monitor is present.

What exactly leads you to believe that this "magic key" expects a monochrome monitor? And why did you put "hercules emulation" in your subject line?

Old application and Hercules mode

Looks like it just doesn't work on recent DOSBox versions, though it did on older ones. Maybe it's been fixed in SVN since 0.74, maybe not.

Even that screenshot says it's expecting a monochrome card, so yeah, you didn't word your question very well.

Which part of the source code corresponds to this change?
Thanks
Jack

Fixed in SVN by revision 3617. The issue was first reported for the hercules version of Spacewar, but also applies to Magic Key.

Thanks ripsaw8080