If you want to make a health bar (or power bar) you can try:
HealthBar.width=(Self.InitialWidth + (Player.Health-PlayerMaxHealth)*(Self.InitialWidth/PlayerMaxHealth))
InitialWidth = instance variable
You could use setcolor effect:
with function you can set color
*compare player.health > 66/100*playerMaxHealth then set color "green"
playerHealth is between 66/100*playerMaxHealth and playerMaxHealth*33/100 then set color "yellow"
playerHealth <33/100*playerMaxHealth then set color "red"