There are people who can achieve huge success in life, while adding a bit of fun and a splash of colour to this increasingly grey world.

This quote is saying that some people have the potential to experience great success, while also making their own life and the life of those around them more cheerful and positive. They live their life enjoying the colourful aspects of the world and bringing that joy to other people. Despite life being often difficult and stressful, they can still find ways to make it enjoyable and more meaningful through their attitude.