This is current/amd64, making a screenshot with
xwd > file.xwd
X Error of failed request: BadColor (invalid Colormap parameter)
Major opcode of failed request: 91 (X_QueryColors)
Resource id in failed request: 0x0
Serial number of failed request: 114
Current serial number in output stream: 114
That's a window dump of chrome.
A window dump of xterm or mupdf works just fine.
I am not sure where the error is.
Does chrome use some Colormap that xwd cannot cope with?
Does it make a difference to xwd which window it is dumping?
Jan