What is it called when one human eye is seeing brighter color than the other?
here is forum discussing similar effect ,

where as similar problem which leads to double vision is single eye is called monocular Diplopia. 

There are two possible causes discussed in that forum. One is a cataract or an early indication of a cataract, for which a vision specialist visit is recommended.

Another solution is much simpler one of the pupils is more dilated than the other:


  The way your eyes see colors changes throughout the day, not dependent
  only on external conditions. Try this: gently press the palm of your
  hand against one eye (closed), for about a minute; leave the other eye
  open during this time (feel free to blink, of course...). Now, look at
  the world with one eye covered (for a couple of seconds), then the
  other — the eye you help closed will see things as quite more
  saturated, partly because you've fostered its pupil to dilate in the
  time during which it was shut. I recall being confused by this when I
  first started noticing that, upon awaking, either eye would see colors
  differently from the other; simply, the eye rested on the mattress
  would be seeing colors with greater saturation.