A Gradient Settings screen is available through the 'Layers > Background > Gradien' menu for the gradient background layer and through the 'Spirals Settings > Angle spectrum' menu for spiral drawings.
With the small 'Detective' button located in the top-right area of the screen, you can have a possibility to preview your gradient in the larger box than the gradient slider itself.
You can use extra settings for the background layer gradient as gradient type (Linear, Radial or Angle) and gradient rotation.