An easy system to help developers implement a colour changing crosshair, depending on the element they are looking at.
In this example, the crosshair can change to a different sprite and colour when they aim at an enemy, a friendly, or at an item they can interact with. Included is documentation on how the system works, with a step by step breakdown for you to follow and use to incorporate it in your game.

Check out the details from the Unity Asset Store: https://assetstore.unity.com/packages/tools/camera/dynamic-crosshair-color-change-144330