Something is telling PSE that the document you want to add the screenshot TO is grayscale. You said you are working in a history text page —could you take a screenshot of PSE for us with that text file in it - being sure to include the layers panel in the screenshot. Also, while you’re in that text page in PSE, take a screenshot of the Image Mode menu showing that the mode is RGB. Then drag the screenshot into that open doc and check the Image Mode again. If it has changed to it Grayscale or BMP, change it back to RGB.
From the research I have done, this does happen occasionally. It seems that if you have copied the text that’s in that page from something else and then pasted it into PSE, sometimes something about that gets stuck in the computer’s clipboard, sending false info to PSE.
Heres the article I found — it applies to both the full version of Photoshop and PSE.
In this article, I show you how to fix the grayscale color problem in Adobe Photoshop. It’s a common problem that many people are having, let’s have a look.
learn-photoshop.club