One of my favorite automations is my "temperature lamp." HA takes an average temperature, humidity, and illuminance from various outdoor sensors around my property. I have a template sensor that uses these values, then gives me a "feels-like" outdoor temperature. Another template sensor takes this "feels-like" temperature and converts it to a percentage between 0 (freezing) an 100 (> 120 degrees F). It uses this percentage to calculate a value between blue and red on a perceptually-uniform colorspace (CIELAB) and spits out an RGB value. An automation watches this RGB value and applies it to a RGB light bulb in my living room.

The result is that I have a light that displays what the temperature "feels like" and changes color in a way that people perceive as matching the temperature. So if the lamp looks "kind of blue" it's going to feel "kind of cold" outside. If the bulb looks "kind of red," it's going to feel "kind of warm."

I set this up for fun, but it's actually ended up being really useful. Before we leave the house, we can just glance over at the lamp and know if we need to put on a sweatshirt or a coat, or maybe leave the outerwear at home.