PDF thumbnails in media-browser get wrong colors

When I upload PDF to media-browser I sometimes get

  1. the PDF symbol as thumbnail
  2. a correct thumbnail of the first page of the PDF (expected result)
  3. a thumbnail of the first page with inverted colors

Result 1 occurs on a different machine then Result 2 and 3 but it is the same sitepackage used.
Result 3: I thought color schema of the PDF could be a problem. But there it does not make any difference between RGB and CMYK documents. Both can get wrong colors. But there are thumbnails that have the correct color.

How can I try to get rid of Result 1 and 3 so that all thumbnails are as expected?

Problem 1 is fixed!

The documentation on Introduction — Neos Media dev-master documentation gave me the hint. My settings for Neos: Imagine were set to GD. This caused result 1 on the development server but on the staging and live server the same setting changed to Imagick which leads to result 2 or result 3. On development server now is result 2 which is fine.

So how to get rid of result 3 on staging and live?