Relabels layers and groups (Win: Ctrl+Shift+Space, Mac: Option+Space).
Unfortunately, labeling layers using AE's label dropdown is non-visual and a bit time-consuming. When executing Relabel Layer/s, however, a panel comes up with all label colors that you can see visually. Click on the desired color to apply it. When a group layer, or the group header, is selected and a label color is applied, the whole group gets relabeled. When the setting Label Layers Outside Groups to 'None' is deactivated, you can relabel non-group layers too.
You can close the relabel panel by either clicking on empty space on the panel itself or by hitting Escape.
To change a label color, you can Shift+Click on a color. This will open AE's color picker. After choosing a color, you will return to the relabel panel. If you want to apply the color directly after choosing it, Ctrl+Click or Cmd+Click on it.
An English name for the new label color will be saved automatically, based on the color picked. If you want to have control over the new color name, go to Settings / Miscellaneous and enable When changing a Label Color, ask for new Color Name.
If you Alt+Click or Option+Click on a label color, AE's label preferences will be opened.
Button on the Relabel Panel to change Outside Labeling Setting
On the relabel panel, you can quickly change the setting Label Layers Outside Groups to 'None' in Active Comp. This is useful when you open up another comp and want to set a specific setting for it. For comps with a lot of groups, it is recommended to label layers outside groups to 'None' whereas comps primarily with layers and not groups, you might not want to label layers outside groups to 'None' since you otherwise couldn't tell those layers apart.