I'm wondering if anyone has started noticing issues with responsive emails on Samsung Galaxy devices running Android 4.3?

As a follow up inquiry, I've been looking for a clear answer(s) all over and haven't had any luck. I hope one of you can help!

  1. What is the difference between the "red envelope" stock email app and the "yellow envelope" stock email app?
  2. Is the stock email app on the Galaxy S3 and S4 a Samsung app and not the stock Android app?
  3. Is that the difference between the red and yellow envelopes? Red=Samsung; Yellow=Android?

It's been really frustrating to sort this all out, so any help is greatly appreciated.

Thanks in advance!