Leaf problem beginner

[Bona]

Dear Friends,
this is my first time of growing.
have some trouble with some leafs though.
look at the photo and you can see that the “problem” comes from the “vains” and not from the in between. Otherwise all my plants looks like the other photos. You are most welcome to comment on these, but they seems healthy to me, like I said first time. Maybe next time it will be better.

 

[crucialbunny]

When was the last time she got some magnesium? You might try a little epsom feed. Beautiful colas.

 

[ChadWestport]

Its odd that such a bad looking leaf is on such a good looking plant. Definitely have some interveinal chlorosis, could be magnesium as Crucialbunny mentioned. Have you been giving the plant additional phosphorus in flower?