{
  "builders": [
    {
      "type": "docker",
      "image": "ubuntu",
      "commit": true
    }
  ],
  "provisioners": [
    {
      "inline": [
        "echo hello"
      ],
      "type": "shell"
    }
  ]
}

docker output will be in this color.

==> docker: Creating a temporary directory for sharing data...
==> docker: Pulling Docker image: ubuntu
    docker: Using default tag: latest
    docker: latest: Pulling from library/ubuntu
    docker: 124c757242f8: Pulling fs layer
    docker: 9d866f8bde2a: Pulling fs layer
    docker: fa3f2f277e67: Pulling fs layer
    docker: 398d32b153e8: Pulling fs layer
    docker: afde35469481: Pulling fs layer
    docker: 398d32b153e8: Waiting
    docker: afde35469481: Waiting
    docker: fa3f2f277e67: Verifying Checksum
    docker: fa3f2f277e67: Download complete
    docker: 9d866f8bde2a: Download complete
    docker: 398d32b153e8: Download complete
    docker: afde35469481: Verifying Checksum
    docker: afde35469481: Download complete
    docker: 124c757242f8: Download complete
    docker: 124c757242f8: Pull complete
    docker: 9d866f8bde2a: Pull complete
    docker: fa3f2f277e67: Pull complete
    docker: 398d32b153e8: Pull complete
    docker: afde35469481: Pull complete
    docker: Digest: sha256:de774a3145f7ca4f0bd144c7d4ffb2931e06634f11529653b23eba85aef8e378
    docker: Status: Downloaded newer image for ubuntu:latest
==> docker: Starting docker container...
    docker: Run command: docker run -v /home/mike/.packer.d/tmp/packer-docker748549162:/packer-files -d -i -t ubuntu /bin/bash
    docker: Container ID: 8a9842afa7f2d495293832c8f50cb3ca0bbbcc48642014670f401bcfe2fe21a4
==> docker: Using docker communicator to connect: 172.17.0.2
==> docker: Provisioning with shell script: /tmp/packer-shell886744952
    docker: hello
==> docker: Committing the container
    docker: Image ID: sha256:9fa2455918ddc0578e06c3b6e847eb6623e76878589af327b06e25ab02bd7b81
==> docker: Killing the container: 8a9842afa7f2d495293832c8f50cb3ca0bbbcc48642014670f401bcfe2fe21a4
Build 'docker' finished.

==> Builds finished. The artifacts of successful builds are:
--> docker: Imported Docker image: sha256:9fa2455918ddc0578e06c3b6e847eb6623e76878589af327b06e25ab02bd7b81