Hello @Fernando D'Amico,
There's no way how to change the color of Comments font separately. I'm adding your request to our wish list.
Comments font colour changes accordingly with the post text colour. You can change it in your Post page Design settings. I advise you to change 'Text style and colour'. But it's interesting because in your case post text shouldn't be visible as well.
Can you give me your website address? It would help me to address the issue better.
By the way, if you don't know how to access post page design settings, read here: https://support.wix.com/en/article/customizing-the-post-page-in-the-new-wix-blog
Thank you very much for the brief reply. The text color of the post is white and in the comments it is black.
Please contact Wix customer support: email@example.com to get assistance on this.