I do not think it is possible to change the number of levels or the colors etc.

This is how I use them:

Next actions (to be done by me) or Waiting for actions (to be done by others):
Turquoise = no need to check routinely every single day (only a weekly review is mandatory)
Blue = check routine every morning
Red = check every time I aven look at the Next/Waiting lists

Someday (that I am not sure yet whether they should be done): Same principle as above but with different time scales:
Turquoise = Every six months or so
Blue = Every week
Red = Every single time I look at teh Someday actions (this is usually extremely tempting things that I have not decided yet whether I dare to do)

The No Priority setting I use for an entirely different purpose - to indicate subsequent, dependent actions that cannot be done until some other actions have first been completed.