[mdjlucan]

Please look a bit yellow. What can this be?

[Aunt Sally]

I think you forgot to add the picture 

[mumofstig]

Just give them a liquid feed, that'll perk them up, I used Miracle-Gro, but any flower fertiliser would do 

[mdjlucan]

Tomato feed, okay?

[mumofstig]

Tomato feed is best once they've started flowering,
If that's all you've got, and the beans haven't started flowering yet, I'd only use it at half strength.