With visualisation, use what is working for you each time and feel free to experiment with colour and light. You can play using the imagination with the intention of bringing a deep calm to the mind.  
And remember, with any meditation practise it's important to throw away your expectations about how it should feel and what you should experience. Every meditation is different, every moment is unique. All you have to do is be curious and kind and allow each moment to be as it is (and this includes noticing that you are really battling with this moment or if you notice that you keep getting completely distracted!) It is a training for the mind and an opportuntity to learn about the mind, body and heart interaction. What do you notice?