When switching to night mode and a user opens a post, the font color of the post also changes to white which I'm assuming is because unlike steemit this site has a white overlay over the post when in night mode. This is what I assume is a simple css issue.
Upon investigation the css files, I narrowed it down to
.theme-dark though it would cause all fonts in nightmode to go back to black which I think is a bad idea but it is a start.
I hope that my thoughts on the problem will help in solving the issue.
Also in night mode all the colors remain to be in "steemit" colors which I understand is because the night mode is probably the least of the priority but mustn't be overlooked .