When using spot colors, the color palette will turn black and white. What is its function?

Question

The color palette will become black and white when using spot colors in Photoshop. When using a white brush to paint the spot color layer, the spot color layer image will disappear, which is the opposite of the image appearing when the mask white brush is painted. What is the meaning and function of black and white painting in the spot color palette?

Stephen Marsh · Accepted Answer

Alpha channels are greyscale, ranging from white to black with grey values in between.

Spot channels are a special type of alpha channel. As they are for print production, they use a subtractive colour model, where white = 0% and black = 100%.

Colour values are assigned to the spot channel via it's properties rather than by using a colour swatch or mixer values as would normally be the case for RGB/CMYK/Lab colour pixels.

There's a lot of room for error with spot channels if you're new to them.

What are you doing and where and how will the spot channel be used?

https://helpx.adobe.com/au/photoshop/using/channel-basics.html

https://helpx.adobe.com/au/photoshop/using/printing-spot-colors.html