Header bar colour change
Header bar colour change

Change to match the Woolaroo green colour.
GoogleCloudPlatform/woolaroo-language-learning-app,GoogleCloudPlatform/woolaroo-language-learning-app,GoogleCloudPlatform/woolaroo-language-learning-app,GoogleCloudPlatform/woolaroo-language-learning-app,GoogleCloudPlatform/woolaroo-language-learning-app