Closely relates to MC-241321. It likely also relates to MC-197123.

The bug

The red oval displayed around the screen when the player is close to or past the world border is only present in the Fancy and Fabulous! graphics settings.

According to this 2014 post on Twitter by Dinnerbone, the fast graphics option is only intended to change the transparency of leaves as well as rain particles, neither of which are relevant to the presence of this effect.

How to reproduce

1. Use Fancy/Fabulous! graphics
2. Approach the world border
3. Note the redness around the edge of the screen
4. Now switch to Fast
5. Notice there is no longer any such redness

Expected results

In line with Dinnerbone's comment, this red effect would still be present even in Fast graphics.

Actual results

The effect is absent entirely.