In Splatterhouse (2010), outlines are used as a quick way for the player to understand certain changes in the creatures faced in the game. It also deals with the condition of the weapons in the game.
When a creature has a red outline, it means that they are ready for a Splatterkill.
A yellow outline means that Rick is "locked on" to a certain creature.
When the creature has a green outline, it means that it is being protected by the magic of an Aegis.
A purple outline means that a creature has been enraged by the magic of a Teratoid.
The weapon is in excellent condition
The weapon is being to break.
The weapon is at the breaking point.