PSP 2019 ULT - Color Changer to Gradient

[hartpaul]

The Color Changer was introduced in X1

The color boxes in your Materials palette are labelled :
Small boxes - Foreground and Stroke Color and Background and Fill Color.
Large boxes - Foreground and Stroke Properties and Background and Fill Properties

The small boxes can only have solid colors, The large boxes can show colors, gradients, patterns and textures.

There are at least 5 ways you could attempt to change a black border around an image. These include Flood Fill, Color Changer, Gradient Fill, Color Replacer and Change to Target Brush .
The OP seems to remember that they used the Color Changer to turn a black border into a gradient but I believe they have confused it with one of the other tools.

As the Color Changer seems to operate only using the small color boxes then it can only produce a solid color fill for the border. As well the Color changer does not work with Black or white as the border - it must be a solid color.
Associated with the Color Changer are the Flood Fill, and the Gradient Fill both of which will change a black or any color border to a gradient as shown:

Color Replacer - will work with any color border and can be brushed on in chosen places or completely using the Replace All pixels button.

Change to Target brush has four modes - Color, Hue, Kightness and Saturation. The only one her that makes a change with a black border is Lightness mode

With a colored border - Color changer uses the small solid color Foreground and Stroke box. The following diagram shows What the change to target brush does .

Conclusion :
To replace a black border with a gradient - Use Flood Fill, Gradient Fill or Color Replacer
To replace a colored border you can use - Flood Fill, Gradient Fill Color Replacer and Change to Target with Mode Color or Hue.