I bought a bag of those Bartlett ‘Purple Majesty’ potatoes last weekend. Instead of mashing them I made chips (well… not real chips, but part-boiled chunks that I then shallow fried to make them taste a bit like roast ones). Purple potatoes taste, believe it or not, like white ones. In case you think something nasty has been added to make them purple (like the potassium permanganate the chemist used to put in the meths I used to buy), purple potatoes are natural, and it wouldn’t surprise me if some of the first potatoes that arrived here from the Americas were not white but purple (note that I refrained from saying ‘first brought here by Walter Raleigh or Francis Drake’, as this is the stuff of legend. They were probably brought here by botanists. Because that’s what botanists did). The purple Bartlett ones are purpose-bred, and are said to contain more antioxidants and other goodies than white ones.
There are also purple carrots*. I remember reading somewhere that the red/orange ones were originally bred from purple ones. Not a lot of people know that.
* Just looked it up, here