[ryandrake]

You can still tell whether it is an iMessage or text message without replying and observing the color. Long-press on the incoming message. If the menu shows: Reply, Copy, Translate, More… then it is an iMessage. If the menu shows: Copy, Translate, More… then it is a text.

[MarkSweep]

The text input box will also say whether it is a text message or iMessage before you start typing anything.

[y2bd]

That's cool, didn't know that Apple didn't try to somehow shoehorn threads into SMS (like they currently do extremely poorly with tapbacks and stickers)