Authentic bruschetta

Hi,

I've eaten tons of bruschetta so far but have all been made differently. I wanted to create a recipe for myself and stick to it, but doing research online has made me a little confused. I've been doing research for authentic tomato and basil bruschetta. Tons of authentic recipes differ in one thing particularly: onion. My question thus is: does onion go in an authentic bruschetta? and if so, does it matter if its yellow or red?

Thank you in advance :)

bon appetit