Touched by: This implies emotion or feeling, often positive.
* *She was touched by his kind words.*
* *The story touched my heart.*
Touched with: This can imply a slight amount of something, like a color or emotion.
* *The sky was touched with pink at sunset.*
* *His voice was touched with sadness.*
Touched on: This means to briefly mention or discuss a topic.
* *The speaker touched on the importance of education.*
* *We only touched on the subject briefly.*
Touched at: This is less common but can be used to convey a sense of being affected by something.
* *He was touched at her concern for him.*
Touched in: This is also less common but can be used to indicate that something has been influenced by another thing.
* *His art was touched in by his travels.*
Touched up: This implies making minor improvements or adjustments.
* *The photographer touched up the photo before printing it.*
Touched down: This is used specifically for airplanes and means to land.
* *The plane touched down safely at the airport.*
It's important to consider the meaning you want to convey when choosing the preposition. The context will often guide you to the most appropriate choice.