Should work in any RPGMaker.

You're going to need a variable. Call it "Hero HP".
You're going to need another variable. Call it "Hero Max HP".
You also need a switch called "Cutscene" (you'll see why later).

After setting these up, make an event on every map you need this tinting on that is a "Parallel Process" and has the following eventing:


After setting this up, remeber that the "Cutscene" switch needs to be turned ON at the start of any cutscene and OFF at the end of it. This will allow you to tint the screen during cutscenes without having this event mess around with it!

If you want the same to happen in battles then this is a simpler proposition. First, in every battle, create a battle-event that is triggered by the Hero's HP being between 0% and X%. It should simply look like this:


Then make a second battle-event that is triggered by the Hero's HP being between X+1% and 100%. It should look like this:


The X value is the value you want the tinting to change below. It should be set to the percentage you want, not a raw value!

You could just use a common event script, it would replace the need for adding a new event in every map location.
Otherwise great tutorial, it really helped.

You can also use varying shades of red (or reddish-orange) to make it more gradual and look better.