Question
Hi, i've 20 or so red carpet roses which have been bursting with red flowers, but
they have all turned pink now, even the newly opened ones.  I live in Auckland,
NZ.

Answer
There are two main reasons that a rose will change colour completely. One is that it has reverted to another rose in it's background or it is the soil that has changed the colour. Acid soil is known to have an effect on the colour of red and it will even darken pink. It might be a wisdom to sprinkle a handful of lime around just one of the plants and see if that gives you back the original colour.
There are 8 different colours in the series. The first, and in my opinion one of the best, was the Pink Flower Carpet, then Appleblossom is another very good one is Flower Carpet Pink Supreme. As you can see many were bred and introduced so possibly there has been a reversion in yours. If the lime doesn't have any effect then it has definitely reverted to another rose in the series or one that is in the background of their breeding. If you have just purchased them, they I would mention it where you got them as they might replace them for you. They certainly would be interested in the change of colour. Hope this helps.