finchmix22 got it covered really nicely!
Fabulous photos, Deborah! (And what's up with the crazy jelly bean egg? That's a nutty looking one!)
I've got to get some good photos of my own to make up a post on my finch site!
It's really easy to see the difference when you can compare (vs. trying to determine an egg's fertility alone.)
So just to summarize, without any candling (just a bright light), you'll see....
- newly laid eggs can be rather translucent in appearance OR they can have a yellowish tinge (from the yolk.)
- mid way through incubation, they lose their translucency and take on a white "eggshell" appearance. (The same slightly shiny, slightly matte finish of eggshell finish paint.)
- 3/5 way through incubation, they can sometimes take on a slightly pinkish tone. (This is from the blood vessels).
- at the tail end of incubation, they become obviously bluish/grey in color.
Here's a good photo that depicts the yellowish tinge in a new egg. You can see the yolk clearly at the middle of each egg on the left row, while the older infertile eggs on the right look whiter. Those are Ivy's enormous eggs!
Of course, it's not as reliable as candling. You can only tell if the egg was fertile at some point in time with this method; it's impossible to know if it's still alive and growing. And the early stages of development can be difficult to detect, as the vessels are small; once they grow in quantity and size, it impacts the egg's color.
If you're new to candling, I have some good comparative photos here:
http://wp.me/p4JWrl-8w