Fed mine the listed amount for iris purple. I suspect I'll get a different shade, here are my noted feeds vs "new feather" messages.
4 berries
1 valfruit
"rubens begins to grow new feathers"
2 berries
new feathers
1 valfruit
new feathers
1 berry
new feathers
1 valfruit
new feathers
1 berry
new feathers
1 berry
new feathers
1 berry
new feathers
1 berry
new feathers
1 valfruit
new feathers
1 berry
new feathers
1 berry
new feathers
1 berry
new feathers
1 berry
new feathers