XPLMDrawTranslucentDarkBox
From X-Plane SDK
XPLMDrawTranslucentDarkBox
XPLM_API void XPLMDrawTranslucentDarkBox( int inLeft, int inTop, int inRight, int inBottom);This routine draws a translucent dark box, partially obscuring parts of the screen but making text easy to read. This is the same graphics primitive used by X-Plane to show text files and ATC info.