Gander with pale beak?

[Goosebaby]

I’m new here, I’ve had geese for about 9 years, I have 7 geese but one of my ganders Parsnip has an abnormally pale beak, the rest of the flock have nice vivid orange beaks, his is yellow.

I’m feeding them all a blend of grains, corn, millet, milo, wheat, and sunflower seeds, “though they all refuse to eat the sunflower seeds” along with being on pasture grass all day.

Parsnip has gone through emotional trauma, he lost his brother who he was inseparable with last fall and has been lonely and stressed most of the year since, I tried pairing him with two young females immediately, he isn’t hostile to them but is mostly uninterested, he and his father Leo have managed to bond just this last month and a half and are both now happy and getting along great.
Parsnip normally is pretty robust and has never been ill, so this pale beak he’s developed has me concerned.

Any thoughts about what this might be, how it was caused and how to fix it?

 

[Goosebaby]

Parsnip in the forefront with his dad Leo.

 

[Goosebaby]

Also I forgot to add...

Parsnip is 7 years old.
His droppings are fairly runny but don’t have an abnormal amount of urates, they’re mostly brown so I don’t think he’s been eating as much grass as he normally used to.
He has lost weight over the summer.
He’s eating and drinking normally though.
He’s been feeling down since he lost his brother, a little quieter than usual.

 

[Goosebaby]

Update, Parsnip is still losing weight, any ideas? Please?