Which feature distinguishes adult Peregrine Falcons from immature ones in terms of color?

The distinct coloration that sets adult Peregrine Falcons apart from immature ones is primarily the blue-gray plumage found on their backs. As adults, these falcons exhibit a much more uniform and refined coloration characterized by this bluish-gray feathering, which provides them with a striking appearance.

In contrast, immature Peregrine Falcons display a more varied brown and streaked plumage, which helps them with camouflage in their younger stages. The blue-gray coloration of the adults not only signifies maturity but also indicates their readiness for breeding and territory establishment.

The other options do not accurately represent the characteristics of adult Peregrine Falcons, further emphasizing the significance of the blue-gray coloration as a primary distinguishing feature.