View appears transparent over tableView, whatever alpha channel

I have a view in storyboard, with a tableView and a coloured UIView.

The UIView is declared after tableView, so it appears on top of tableView.

However, it appears semi transparent over the tableView.

In addition, I cannot set its alpha channel to values other than 1 or 0 (e.g., 0.9)

But if I create the view programmatically, the view if fully opaque as expected.

What am I missing ?