Yea that's how you make a gradient for "Background", a one sided square, or a sphere.

k = (V - bottom_of_gradient) / (top_of_gradient - bottom_of_gradient)
Blend(color1, color2, k)

You can also rotate the gradient up to 90 degrees by using Blend(U, V, rotation) instead of V. For full rotation, you can use trigonometry.

But as you point out, doing this on the "Background" is not 3D - it is 2D. There is no way to make the gradient obey 3D perspective as you move the camera around.

And I still don't get the point. We can use nodes to fill the "Background" with anything we want, but if you save with transparency, you pretty much have completely discarded it, right? Why bother programming a background if you're going to ignore it in post?

Also, for Gareee's moon, if we use the transparency version of the moon shader that I made, so that it reveals the background instead of drawing the dark side of the moon as black, it too will be discarded when you save with transparency.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)