If you are a web designer then you will already know how important visuals are to a website creation process. Every website should be visualised prior to programming to ensure that all parties (i.e the client, designer and programmer) agree on how it should look and function. At this stage it is relatively easy to change things around but if left until it has been programmed it can take a lot longer to do incurring more costs for the client or the web management company.
Ideally present your client with a few variations of the website visual to allow them to see how it could look. I would advise showing them on a computer screen (not just printed visuals) as the colours often look different when printed.
Colourways can make a big difference to the way a website looks so you may want to experiment with these to show your client.