#1). BIG HOLE. You want the biggest "peep" you can get to let all the available light thru... Some use these in regular light on dangerous game rifles and call them "ghost rings." Your eye will automatically center the thing you focus on (front sight I hope) in the strongest light in the circle. So beware strong light from the side if the shot is very long.
Jack O'Connor used to talk of buying an expensive rifle with an expensive peep sight, unscrewing the tiny hole peep disk, throwing it in a drawer, and going hunting with the threaded ring...
#2). Modern tricks... red nail polish on, flourescent orange paint on the front sight??? White? Your call. You want all the help you can get picking up the sight in the low light. If you have the inclination and bucks there are the radium radioactive front sights that glow in the dark... From there, you might want to put paint around the inside of the ring to help you there, but it is tricky. This is alot of personal preference and then practice. This is CRUDE and you have to learn to use it as best you can with whatever quality of eyesight you have. LUCK.