GtkScintilla::marker_set_back

void marker_set_back(int marker_number, int back);

Set the Background color of a marker, for markers table, see marker_define()

// defining background color of marker 1...
$scintilla->marker_set_back(1, hexdec('0000FF'));

// defining background color of marker 2...
$scintilla->marker_set_back(2, hexdec('0000FF'));