Red, blue, black, green design diagram

Quick answer：

A 'red, blue, black, green design diagram' typically refers to a visual representation that uses these colors to convey information or aesthetics. It can be found in various fields such as graphic design, urban planning, and data visualization. In graphic design, such a diagram might use these colors to differentiate between elements or convey specific meanings. In urban planning, it could represent different zones or areas. In data visualization, it might use these colors to indicate trends or categories.