This was originally an RGSS3 script but it's ported to RPG Maker MV.
Screenshots(Note: Yanfly's scripts were used during development. It will still work without it.):
Installation and setup:
1. Place the plugin file to your project's js/plugins folder.
2. Place this plugin below any plugin that changes HP Bars as well
(such as Yanfly's Core Engine). If you don't have any of these on your project,
you can place it anywhere.
3. After turning it on, save and playtest. If the game didn't crash after opening the menu and you can see the bars green, the plugin is installed properly.
If you wish to use the HP bar colors set by the other script, turn on the compatibility mode by setting it's value to true. Compatibility mode will simply ignore Normal HP Color 1 and Normal HP Color 2 and will use the preset color (or the other plugin's color, if it rerouted the selection).
Configuration of the colors is explained on help.
Add-ons are found here.