Libreoffice Headless PPTx File convert to PDF producing background color to the text in the output

Using Libreoffice headless --convert-to pdf command in the Ubuntu system,
the converted pdf is getting added with the background color to the text.
and this is happening for few files only.

Here is my input command
libreoffice --headless --convert-to pdf --outdir /mydir/ /localpath/file.pptx

May I know the reason and the corresponding solution related to the same?