Hi. If I select the color paper panel, the panel does not display. So, I can not change the color.
Hi Robert, you mention 'color paper' panel...I am not familiar with such a panel...can you provide us a screenshot of it?
As Fuzzyboot s mentions, there is a 'color' panel (which has the color wheel) is this what you are looking for? If so, they are correct--the panel may be somehow positioned offscreen, in which case if you don't have many customizations to your UI layout just go Window > Layout > Default to 'rebuild the default layout'.
If that still doesn't work maybe just hold shift at launch to reset your workspace and the panel should be visible again.
Also it might help to know when the panel disappeared, if you happen to remember the steps!
Well, and to be fair, there's also a Paper panel, which can also accidentally be disappeared. The closest I know of to a "colored paper" panel is what display when you create a new image where you can select the color and paper, although you can get close by lifting the layer (which I think the only option, at least of 2020, is to lift the canvas to a Watercolor layer, and then select Convert to Default Layer or Convert to Reference Layer) and then setting the Canvas layer paper and color.
Yes, good points. Maybe Robert will give us more info...