[Willie_Dynamite]

Some foodstuffs company whose name I've forgotten tried to introduce yellow ketchup in my area a couple of years ago, but they failed pretty badly. I bought a bottle, and while it tasted just like the the red stuff, it just didn't look right. My 5 year old niece just flat out refused to eat it.

[Groxx]

Yeah, and remember the green (and purple) Heinz sales? They didn't last long.

At the cost of duplicating my other comment, it fits here perfectly:

I hate to cry conspiracy theory, but I really do think that American culture in particular has been groomed to think and eat this way by food suppliers. When you can color / bleach something, you can hide flaws.

[jerf]

"I hate to cry conspiracy theory, but I really do think that American culture in particular has been groomed to think and eat this way by food suppliers."

I tend to consider conspiracy theories a last resort. It is not that they are never true, just that reaching for them first is a mental crutch. In this case, I would suggest that given the importance of food, one would rather expect evolutionary considerations to dominate how we feel about food colorations. It may be true that making food "look good" can be used to hide flaws, but I seriously doubt the concept of "looking good" comes from training. I would imagine it mostly comes from genes and common-sense-type-training.

(I assert this without proof, which is why I mentioned my conspiracy-theory metric. My point is that I don't see a need for the conspiracy theory choice here.)

[Groxx]

Yeah, I generally agree. And the evolutionary standpoint makes sense, and is the logical counter to this. My main focus there isn't that we equate the two, it's that there's such a strong connection. At least, as far as I can see. It could've grown from "that sells better, what if we do this", but it's still kinda strange, and I wonder if it's at least partly intentional.

'Tis just speculation, though. There are plenty of weird / weirder things in the world.

[julius_geezer]

As probably one of very few HN readers to have made my own ketchup (all you need is time, a kettle, and a farmstand, preferably selling seconds), I can say that dark red is your basic ketchup color if you start with red tomatoes. Purple sounds like heirloom, and at farmers market prices you'd be approaching the price per volume of very good wine.

[bricestacey]

I'm not sure you'd ever get purple ketchup even with purple tomatoes. Usually the purple pigments in food disappear after heating them. Do you think that'd be any different in tomatoes?

[_delirium]

I think it depends on the particular kind of pigment. Purple berries typically stay purple when cooked, which is why blackberry pie is still purple, and eggplants stay purple also. Beets turn red, though, since the purple pigment degrades while the red one doesn't.

Not sure where purple tomatoes would fall. Some googling turns up anthocyanin as the pigment, and Wikipedia says it's water-soluble (so would leach out if the fruit is boiled and the water not retained), and changes color based on pH.