What does the shaded pokéball icon mean?
I'm not able to catch any Pokemon, I feed them but my pokéball icon is shaded!
What does this mean, and why won't it let me catch any pokémon?
Solution 1:
That blanked out circle means you have no Pokeballs left, and therefore are unable to attempt to catch a pokemon. To get more balls you will have to either purchase some from the store, or find some by spinning pokestops.
Feeding a pokemon berries will not change this, instead they make it easier/more profitable to catch pokemon when you have pokeballs to use.