Bicolour tomatoes?

I am growing what are supposed to be Maskotka tomatoes, high-yielding hanging basket types.

After a shakey start, nothing is high-yielding this year (also growing Red Alert bush types) but I've just gone out to fetch the first ripened ones in and they are two-tone! Fully ripe and damned tasty but not the solid red they should be. Any ideas? Have I been sold the wrong seed, or is it something to do with feed, compost etc? They get liquid tomato food once a month and have been slow to grow and fruit.

 

Its definitely due to growing conditions.
If its greenback the green part will be hard and inedible.
The calyx looks kind of dead, for a recently picked fruit.

 

Thanks. The smaller one I found between the pots, so that one wasn't picked and was probably there for a few days.

The greeny bit isn't too hard - I've eaten both with no problems, very tasty!