Press the flag. Use the Health slider to change what you game health will be. The RGB color will change in response to your heath!
Shoutout to @Wes64test for the RGB system! BTW it may take a small amount of time for the RGB to catch up with the Health :P Also when you reach 100 from a low value it may glitch for half a sec and show yellow, it will corect itself soon after! Update 11/4/17: Your Health may now surpass 100 and the function won't activate until under 100. In future i will add buttons for increase and decrease.