Pencil icon is smaller than others on Color icon theme

GIMP version: Gimp 2.10.8

Operating System: Ubuntu 18.04

Package: [snap / ppa]

Pencil icon is smaller than other icons on Color icon theme.

Is the bug reproducible? [Always]

Reproduction steps:

1. Choose 'Color' theme via Edit - Preferences - Icon Theme path.
2. Select 'Custom icon size' from the dropdown menu.
3. Change Icon Size to Large or to Huge
4. Check Pencil icon size on the toolbox.

Screenshot