Tejas
Here are a few of the steps I took originally.
First I decided to mark the text as white using the editor. Note that I am using paragraph boxes inside a Row Layout from a Kadance plugin block, to give me a narrower column of text. Although I have also tested without such a feature and had the same problem.
After setting text white I saw that it was invisible against the white background of the editor. I then removed that text colour setting and used the customiser to create a global typography setting for paragraph text throughout the site.
When I returned to the editor the text has remained white, even though all paragraph colour settings have been removed (see exception below).
In this instance I was creating a page, but the same effect seems to appear when creating a post – the entire editor is white throughout.
Here’s the page I was editing…
https://www.sterlingsecure.co.uk/bondevzoneWP/beeland/
Here is a screenshot of the editor page.
I have highlighted some of the text to illustrate the issue, and the B.E.E. heading (not a Header, as that is also invisible in white) has been set to black for visibility here, although it returns to white on the web page.
https://www.sterlingsecure.co.uk/bondevzoneWP/wp-content/uploads/Responsive-in-White.jpg
I wonder if there is some setting that is not being flushed from the database when I was making these shifts in the settings?
As I mentioned originally, I did a test on another site with the WP default Twenty Seventeen theme, white text in the customiser and no playing around with text colour in the editor, and had no problem with retaining colour in the editor.
Hope that helps.