I have a few leghorn hens, and they used to have whitish feet, and now their feet are bright yellow.
That is perfectly normal.
For chickens that naturally have yellow legs (like Leghorns), the legs get very yellow when they are not laying. But when they are laying eggs regularly, their body puts the yellow into egg yolks and not into their skin, so the legs fade.
It's predictable enough that people have used it when selectively breeding good layers: the ones with the palest legs have laid the most eggs in the past few months.
I'm thinking yours probably had the whitish feet while they were actively laying last summer, and now they've had a molt and a nice break that let their legs turn yellow. It takes quite a while (weeks or months) for the legs to fully change color, so you don't see it right away when they start or stop laying.
(What I said above applies to chicken breeds who naturally have yellow skin. Breeds with white skin still lay eggs with yellow yolks, but their skin does not turn yellow when they quit laying.)
My cock used to half bright yellow feet, and now they’re orange brown.
I don't know for sure about him.
The amount of yellow (male or female) can also change if their food has a different amount of yellow pigment. For example, if the feed company uses white corn in the recipe and then changes to yellow corn, the chickens' legs might change color over the next few weeks or months.
Roosters with white legs often show some pink or red in the legs (from blood vessels under the skin), and that can change from one season to another. Maybe the same mechanism could make yellow legs look different colored too?
And of course dirty legs is another possible explanation, as someone else already suggested.
Is that a normal thing? They look fine, and they act fine.
If they look fine and act fine, they probably are fine.
