Before you start to visualise the product, you should have a grasp of the brand identity you are building towards.
Now that the product is coming together, you should take some time to gather the partners branding together. Normally this has already been done be another company, but there is the case where we need to do it ourselves.
Be aware this isn’t a branding sprint, this is simply gathering the message, logo, colour swatches and another already defined materials for your consideration during the wireframe, style guide and pixel perfect stage. Keep it lean and simple and offer suggestions if they haven’t done this stage yet. Things can change between the inspiration stage and the realisation stage so don’t worry too much about this changing.