Hi Tanya, and welcome to the community!

I don’t believe this is possible with Airtable’s Chart Block, but since Vega-Lite supports multi-layered charts and there’s a new beta block for Vega-Lite, I suspect this may be possible. I think you’re after something like this -

Even if this doesn’t help for this requirement, you should get the Vega-Lite beta block if you’re into data visualization and looking for ways to break the bounds of the Chart Block. Even though it’s “beta”, there’s a link to sign up and get access in your account immediately via the form.

Hey, there is no way to do this with the Chart extension and Vega-Lite requires you to write JSON. But it's easy to do with our new extension, Charts & Reports - you can add as many y values as you need and customize the color of each.

https://airtable.com/marketplace/blkwmujNx6HUqfnE0/charts-and-reports-data-fetcher