How can I get darker yolks?

[NJChicken]

We have Bufs and RI Reds. About 10 months old. Have laid eggs all winter. With spring and access to worms I thought that we would see a darkening of the yolks to a darker deeper orange. Our eggs still remain yellow. We feed them Dumour feed and kitchen scraps. Eggs are good size and well formed.
Any suggestions??

 

[MarinMama]

I read that yolks get a deeper orange color from greens...

 

[kscottjoyce]

My RIRs eat grass all day long and lay eggs with very dark orange yolks. The bad news is that if they eat too many greens they get softer shells so I need to give them oyster shell to give them more calcium.

 

[WoodlandWoman]

Yup, green feed does it. Grass or dark leafy greens.