What is that black outline when using power window - curve?

Hi, everytime I'm using curve power window, the black line always appear. Whats that for if there is a white line already? is this something that can be turned off/on?

Thank you.

That is an intentional effect. You can get rid of it if you use the Preferences -> User -> High Visibility Power Window outlines mode.

That is an intentional effect. You can get rid of it if you use the Preferences -> User -> High Visibility Power Window outlines mode.

I don't think that is it, when I turn that on in Preferences it just turns the line green.

[Peter Chamberlain]

You have zoomed in a lot, try drawing the white on a white image and the black shadow line makes sense.