In fix implemented for bug 88276, if you create a text box with "A"
Then you edit it, type "B C"
Select B, make background light purple
Select C, make background dark watermelon (the colors have no importance)
Click outside the text box
I would expect a step by step Undo
Currently, text box becomes "A" with no bg color.
It's not limited to text background colour (thus, adjusting the summary).
Repeat the experiment from initial comment with font colour, click outside the box, Ctrl-Z for undo and ta-da - the whole content of text box disappears.
Interestingly enough, undo more-less works when undoing while the cursor is still inside the text box.