Advice, please!

[TempletonPeck]

An Orpington egg, day 12 of incubation.
The other eggs' dark patches are very dark, and many have shown movement - but this one started off light and has never really darkened.
Unfertilised, or leave another few days to make sure?

 

[Lacy Duckwing]

At day 12 looking like that, it could be infertile. If you want to, you can crack it open to see if there was any growth at all. But be warned, it might smell a little.

 

[SilverBirds]

Looks infertile or died early on.