Overview tiles are generated with wrong colors.
There was a wrong line in the code that was no problem in older versions of ImageMagick library.
This was in line 532, in geoquadtree.c:
status=MagickSetType(magick_wand, TrueColorType);
This line has to be modified to this one:
status=MagickSetType(magick_wand, TrueColorMatteType);
This is part of the overview function, which builds a new tile in the upper level, using the four tiles in the lower level. The problem was that the new generated tile was in RGB format, whereas the tiles in the lowest level were in RGBA format. The overview function expected the tiles in RGBA format, so they weren't well read.
