How do you differentiate between formatted and unformatted text in the composition window?

I use Thunderbird on dark mode, so by default, unformatted text (where I haven't explicitly set text color) appears as white text on a black background in my compose window. The same unformatted text, when sent to someone viewing it in light mode, appears as black on white to them and remains readable. When I use white text in my compose window, it looks identical to me, but remains white when sent and is thus unreadable white-on-white to those using light mode. Is there something in the composition window that indicates whether I'm typing with formatted or unformatted text? (No, the color selector tool does not do this. When typing unformatted text, it displays the last selected colors, regardless of whether they are being used.)

If there's no way to distinguish this, could someone please add a UI element for it?