You could pick up each one, spread the feathers apart, and look at the color down near the skin. It is very common for chicken feathers to be a different color down there, but you never see it when the feathers are laying neatly in place on the chicken. Sometimes you will find different colors on different parts of the chicken.
If you want examples on other people's chickens, look for threads about hens with bare backs (usually from overmating). They often have that under layer exposed. Sometimes it is similar to the color of the outer feathers, but sometimes it is very different, like the white fluff on Jasper.