I know nothing but I found this:
A keet does not usually start incubating (sitting) eggs until the second or third one is laid. They normally lay one egg every other day (and this is the order in which they hatch) until they have laid approximately 6 eggs. For some reason (I don't know based on the information you provided), she didn't lay as she should have. Female keets with eggs or babies only come out to defecate...the male feeds her while she's incubating eggs/caring for babies. So, for some reason, she was coming out more often than she should/was staying out longer than she should. Once incubation has started, if the eggs get too cold, they will die in the shell (if they were fertile to begin with).
The difference in the egg coloration could mean a couple things. Eggs are usually white (and appear thin shelled as a chicken egg or like you can see through them)until about the 5th to the 7th day. At about that time, if they are fertile, they turn a darker color...still white, but "thicker" shelled. This darkness to the egg indicates that something is happening inside, usually a baby is developing. However, the egg will remain dark if/when the baby has died in it's shell. After a while if the baby has died (some type of bacterial infection, etc. inside the egg), an egg might begin to smell bad.
Keet babies only take about 18 days to hatch AFTER incubation has begun. Not 18 days from the day they are laid, but 18 days from the day she starts sitting on them regularly. If she has kicked some to the side, she knows they are not going to hatch (she can feel movement inside the egg if the baby is developing properly). I'd say that if no eggs have hatched yet, they probably won't hatch. If she's still sitting on some, let her sit them out (until she kicks those to the side), and then remove all the eggs.
There are numerous reasons why eggs don't hatch. If this is her first clutch and you want her to have more babies, let nature take it's course. Once all the eggs have been removed, she should lay again in about 10-14 days, depending on the situation. Keets are very prolific breeders, so if this keeps happening (eggs not hatching), there is some reason why, which could be her health isn't good, there is some disturbance(s) going on that keeps her from incubating like she should, there's some type of infection entering the eggs, etc. When eggs are present, do not touch them with your bare hands (use a glove or something). Oil from our skin can clog the pores of an egg. Do not disturb eggs any more than necessary or if you have to disturb them for some reason, replace them EXACTLY as you found them, including the right side up or down (parent birds turn their eggs 1/2 way every 12 hours I believe the number is for proper development of the baby). Do not use cedar shavings or anything else in the nestbox.
Hope it helps