How do I access colors in my library?

I don’t use colors in Libraries much but I did a quick test, and for what you’re doing it looks like there isn’t direct access to Creative Cloud Libraries from the Fill or Color Picker dialog boxes. (You probably noticed that the Color Libraries button in the Color Picker does not connect to the Colors group in the Libraries panel, because they’re not the same thing.) But, there are ways that it can work.

You can take advantage of the old Photoshop workflow of applying the foreground or background color swatch. After selecting pixels, do this:

1. In the Libraries panel, click the swatch you want in the Colors group. That loads it as the foreground color in the Tools panel, so now it is available as a foreground color for any feature. 

2. Choose Edit > Fill.

3. In the Edit > Fill dialog box, click the Contents menu, and choose Foreground Color.

4. Click OK.

That can be streamlined with the Fill keyboard shortcut, so for production efficiency you can reduce this to two steps:

1. In the Libraries panel, click the color swatch you want.

2. Press Option+Delete, the keyboard shortcut to fill with the foreground color.

If the selection is a vector shape layer, it can be just one step: Click the color in the Libraries panel. But that doesn’t seem to work for pixel selections.