The Urantia Book does not assign colors colors for the Paradise Trinity, the Seven Master Spirits, or the Seven Superuniverses.   However, color can add depth to charts and that helps with understanding. 

The individual members of the Trinity can act alone, 2-by-2, or all together.  There are seven possible combinations.  This is why there are seven Master Spirits presiding over seven superuniverses.

Blue, Green, and Red, the primary colors, when combined 2-by-2 make Cyan, Magenta, and Yellow. When Blue, Green, and Red are all united, they make White. 

Though there are other possible combinations, this almanac uses these color associations:

Blue

Rationale for the Trinity color selections

This is an image of a light bulb taken through a diffraction grating.  We can imagine the bulb being Paradise and the spectra being a cross section of the Paradise Sphere circuits.  Light follows laws that originate at Paradise.  The channels through which the Paradise Spheres circulate are something like the grooves on a CD that make a spectrum when angled on a light.  In the above grating image, or when observing a colors on a CD, blue is in the closest circuit to the central light, green is in the middle, and red is in the outer circuit.  Similarly, in a rainbow, blue always colors an inner rainbow arc, green a middle, and red an outer arc.

These are some color analogies that lead to the almanac color convention.