Which onions to use and how to cook them for an Indian curry recipe that specifies "fry until deep pink"?

I own the same book and was similarly surprised when I read that instruction, but in the section on ingredients, the author does mention a particular variety of onions called pink onions. The mention is on pg. 32, and there is a picture of a pink onion on the upper left of pg. 34.

Here's an excerpt from pg. 32:

"The longer the onions are fried, the browner they will get and the deeper the color of the curry will be... When the onions are fried until only light pink in color, they will impart a sweetish taste to the curry. Certain varieties of onion, like Spanish onions, are too sweet to be appropriate for curry-making. The most appropriate from the taste point of view are the French and the small pink English."

From 50 great curries of india

I've never seen pink onions in any of the local markets (in northwestern US), I used white onions and sauteed them just to the point of browning. The recipe turned out fine, but it's a lot of onion. (The recipe calls for 2 large onions, finely chopped. It's a recipe that produces 2 servings.) Personally, I'd go a little lighter on the amount of onion or use yellow onions (despite the author's recommendation against Spanish onions), but that is just personal preference from a Western palate.

Note: it looks like the current printing of the book is different from the one I own, so the page numbers I cite may be off, but if you search inside the book (on Amazon) for "pink onion" you can see the page I've cited and the picture of what the author calls a pink onion.

Pink onions are produced for India by Indian farmers. They are actually a hybrid cross of a red and a yellow onion. There are no US or European breeding programs for pink onions. Beware, cooking red onions will make them turn grey.

From some other recipes, red onions sauteed/sweated but NOT browned that then have lemon added turn a deep pink.

It is possible that other onions will do this also...several vegetables go red in acid and blue or blue/green in base.

But once you brown onions, they are not going to pink up. It is not an onion stage of caramelization.

When I roast certain sweet yellow onions (either from a raw state or pre-sauteed, lightly), they often turn a rather bright pink. I am referring to onions that I use in baking bialys or onion pockets or onion rolls (these are old-time New York style favorites). I have heard that they are "on the way to being caramelized" and not to be concerned; they will taste fine. But when I pull out my baked bialys and see the pink centers, it's not very pleasing esthetically. But they are still delicious. Hope that helps.

'Deep pink' means translucent when referring to an Indian pink onion. The Indian onion os closest to pink shallots. Not as sugary as a Vidalia or Walla Walla & not quite as sweet as a Spanish red. Indian pink onions have a 'zest' unlike any onion I recall from the US. I use Spanish yellow onions when cooking Indian food in the US.