Why are my Eggplant fruit yellow?

Picture says a thousand words... Sadly.

Dear Peter,
Last spring I planted a punnet of eggplant, Bonica Hybrid, fully expecting to grow nice purple fruit which was to be used for Melanzana, dips etc.  but to my surprise the attached photo shows what I actually got. I also could not tell when the fruit was ripe as it is all quite firm and if I left them on the bush for too long they rotted.
What went wrong, and how can I make sure that next years crop will be what I want.
My wife has made a nice dip from this fruit although it is slightly more bitter than normal eggplant.
Looking forward to your response,
Kind regards
Alex

We have unfortunately seen this previously, please follow the link for my earlier response.  I have followed this problem up with our seed suppliers to ensure we haven't done anything wrong and that there are no cultural or nutritional issues. No, the international seed producer has grown a bad batch of seed so there are Yellow Eggplants being produced in gardens all over Australia and possibly the world right now.  We have been assured that seed for the 2015 Spring will produce purple fruit.

The yellow fruit is edible but apparently bitter. Alex's wife has the right idea.

I have arranged some replacement plants (not Eggplant at this time of year) for Alex through his local Garden Centre and am happy to offer the same to any gardeners who have encountered the same problem.

Here are some happier pics.  Fresh on our availability list, Argyranthemum.

Argyranthemum Banana Split

C
Agryranthemum Sublime Pink

Agryranthemum Super Double White