Hi Limpieza -
Assuming that you will be playing the game in a closer third or first person view, You can setup your materials for your objects to render in color or Black and White based on a Location-Based Sphere Mask whose size and exact dimensions is controlled in a blueprint. Alan Willard one of Epic’s Tech Artists has put together a great video tutorial for a setup just like this one. He specifically deals with Opacity but you could also change it to deal with color.
Thank You
Eric Ketchum