In Goxel for android version 0.15.1, the Color Picker tool is broken. Even on a fresh project, it refuses to pick colors. On version 0.14.1 it works as expected.
Demonstration: https://drive.google.com/file/d/1Wai6F2HqP8uQxERmJBZqIKNMZuY1kJoG/view?usp=drivesdk