Colors in neovim not shown

Hi all,
I just uploaded my first asciinema cast:

The problem is vim (neovim 0.4.3 to be accurate) is shown somewhat monochrome but it is not. The following screenshot shows the same source file how it has been recorded:

If I download the screencast and replay it locally (with asciinema play 333664.cast) the colors are back to normal, so I suppose the file has been uploaded properly.

Any hints?