Visible light is composed of the colors of the rainbow. Some animals can see colors we humans cannot see, such as deer can see ultraviolet. At one end of the wave lengths is red which is next to infrared which we humans cannot see. At the other end of the wave length is blue/violet which is next to ultraviolet. In the middle is the yellows,oranges, and greens.
Visible spectrum - Wikipedia, the free encyclopedia
In selecting the glass to make a lens and in selecting the coatings for the lens and in designing the shapes the lens designer must make compromises even when cost is no object. Once cost is an object, there are economies to be achieved such as not using ED or Fluorite glass which leads to even more compromises.
If you go to Luepold and read about their mid to top of the line scopes they are advertising that they have improved the blue green color sharpness in their scopes. Well why should I buy a scope with improved color for blue green because unless I am hunting bullfrogs all my animals are brown, reddish or grey. However, if you are one of the people in Iraq or Afghanistan then you might be hunting stuff that is wearing blue/green uniforms and a good sharp blue color would be great for resolving your target.
So from the example of Luepold we can see that a scope lens designer can work to improve certain colors such that those objects are clearer than objects of other colors.
There are other factors that affect the quality of the image you see and the one that we are usually most concerned with at long range is objective size. That is a discussion for another day.
My advice is to take you scope out and look at objects with a sharp distinct edge and see if the color is "true" and distinct at the edge of the object at the ranges you wish to shoot. To be a little kinder to the Fullfield I know very well in the middle of the morning (good light) with snow on the ground I can see through it well enough to tell a six point buck from three does at 350 yards - I just can't shoot a muzzle loader well enough to hit him.
Try to remember that each of us has a little different genetic makeup in eyes and that can range from color blind to limited ability to perceive reds or violets.