Fill a RoundedRectangle with custom color

foregroundColor is the color of the foreground elements…

Namely, the text you type inside.

Are you sure you don't want to set the backgroundColor ?

  var body: some View {
  Group {
  Text("Hello!")
  }
  .background(Color.red)
  }

So:

RoundedRectangle(cornerRadius: 8, style: .continuous) 
.backgroound(Color.init(red: 255, green: 245, blue: 158))

have a look here for more:

https://stackoverflow.com/questions/56437036/swiftui-how-do-i-change-the-background-color-of-a-view

You should use fill().

RoundedRectangle(cornerRadius: 8, style: .continuous)
    .fill(Color(red: 255, green: 245, blue: 158))

Don't use background() for changing the color of RoundedRectangle. It just fills the background of the rounded rectangle rather than the rounded rectangle itself.