I'm sure it's easy, but having trouble changing the gradient color from black to white to a different color. I'm selecting my horizontal header, fill properties, gradient, then the black bar, but I don't get how to change the color. There's no other option but the black bar.

Also, in Page properties, I see how to change the gradient to horizontal, but in Fill properties there's no such option, and the header is changing from white to black vertically.

Thanks!

Amy, click on that black to white gradient bar to open the gradient designer - you'll see an arrow/slider at either end of it. Click on those and your color picker will open up. You can slide the arrows back and forth to adjust how the colors blend.
Back on the fill properties box to the right of the gradient bar is a circle (dial), click on the line and "dial" to change the gradient angle to whatever you want.