Hi,
Yes, it was expected.
Technical explanation:
When displaying JPG image using the 3D card of the computer, the black color (rgb 0,0,0) is converted automatically to “transparent”. As this is not intended, We change this black to a very dark gray (like rgb 10,10,10).
This is not perfect, but on most of the cases, this is not noticeable.
If you are using a PNG, as this kind of files handle the transparency, the problem does not occur.
In the past I was converting all JPG to PNG to avoid the issue. The result was nice, but the size on disk was _a_lot_ bigger (especially on presentations with a lot of photos).
So, if you need a very deep strong black (rgb 0,0,0) please use a PNG image.