needGenerateAcrylic={false} on SSR

[DominykasZaksas]

I am working on NextJS project (server side rendering)

On link
https://www.react-uwp.com/server-side-rendering

Sample code says
needGenerateAcrylic={false} // if using SSR, set this config to false, using fallback color

But that's all the information I can really find.
So I have some questions:

1. Why do I need to set to false even though acrylic background is display correctly with flag set to true
2. Where do I set a fallback colour?

Thanks