The bug

Run the following command with chat colors turned on:

/tellraw @a {"text":"\u00A7d⬛\u00A7b⬛\u00A7c⬛\u00A7a⬛\u00A73⬛","hoverEvent":{"action":"show_text","value":"\u00A7kchat colors on"}}

Note how the squares are colored and when you hover the cursor over the text, the shown text is obfuscated.

Now turn chat colors off and run the command again.

Note how the squares are no longer colored, which is expected behavior. However, also note that the shown text from hovering is still obfuscated. I thought it was reasonable to expect the hoverEvent text to no longer display any formatting. (I also didn't see this earlier, but it is also odd behavior that the shadows behind the obfuscated text don't match the actual displaying text.)

With chat colors on:

With chat colors off:

Expected with chat colors off: