Current bug causes the following:

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=28806

see ox-odt.el file:

...

    (cond

      ((eq fn 'default)

       (format org-odt-src-block-paragraph-format

                      background-color-val color-val))

      (t

       (format

               "

<style:style style:name=\"%s\" style:family=\"text\">

  <style:text-properties fo:color=\"%s\"/>

</style:style>" style-name color-val))))))

...