What natural ingredients can be used to color food blue or green?

According to this blog, you can make blue dye from red cabbage, water, and baking soda. I don't know if it would specifically work on scallops, but I haven't been able to find any proof that alkaline dyes are detrimental to them. The article points out that they work for pastries, though.

Spinach or matcha (green tea powder) could work for green dye. Matcha is already used, primarily in Japan, to dye several kinds of foods and/or drinks and I've personally used spinach to dye Easter eggs.

First, compliments on sticking with natural.

Red cabbage is a natural pH indicator. While you can get it to turn any colour, it will shift in colour if the food pH is not the same as the cabbage.

• You can use blueberries (ha!), blackberries, and Elderberries for various blues (see the note below on why it's hard to get a natural blue).
• For greens, we use basil pesto.
• For reds, there are some edible flowers that do well, obviously beats and raspberries.
• For yellow/orange. Saffron! grind it down in a pestle and mortar and dissolve in a bit of hot water. Note of caution: Saffron at high doses is toxic, but at that dose, you'd be spending hundreds of dollars worth of saffron to get saffron poisoning.
• Obviously you can mix these to get secondary colours.

You can loosely follow this vegetable dye making recipe (obviously leave out the chemicals).

Blue dye in history: Getting a natural blue has been traditionally difficult (and expensive). Artists show Virgin Mary wearing blue because in those days it was more expensive than gold.

Butterfly pea flowers will give a nice blue or indigo color - it is sold as dried whole flowers for making tea with (out of Thailand), and also marketed as a natural blue food colorant or dye. The tea itself is interesting and pleasant, but also mild and herbal in flavor - so should be easily incorporated into or even masked by whatever other flavors you want in your dish. The tea will also turn purple in the presence of acid (like, say, lemon juice) - so you might be able to get your purple coloration from that, if you don't mind adding a lemon taste.

Blue is tricky, at least if you're trying for a taste more neutral than, say, blueberries - so the pea flowers are a good find. And you can brew much more strongly than the picture for a deep color without too, too much extra taste.

If you want a red color (which you can also add to blue for purple) I find hibiscus usually works, it gives a more vibrant red color, while beets usually end up coloring something more pink or itself appearing a duller red, almost maroon, to my eye.

Turmeric or saffron will indeed give yellows and oranges (depending on concentration). Turmeric is also used as a yellow cloth dye, so should have really good staining power for whatever you're coloring. Saffron will get to orange tints if the concentration is quite high (but it is expensive, so only if you already want the strong saffron taste if you're using that much). You might actually try carrot juice for a more consistent and less expensive orange color (or tint your red beet or hibiscus red with yellow, depending on what you want or what you have).

The combination of saffron and butterfly pea flower makes some really beautiful and vibrant greens, from teal to deep emerald - and also a tasty tea, which is what I was doing with it. I had also heard that red onion skins will create a green dye. Other answers mentioned spinach juice and spirulina and the like, so I'll leave them be.

• Annatto seeds will give you another version of yellow/orange.

• Squid ink or cuttlefish ink will give you black.

• Red wine or grape juice sometimes colors foods red.

• Apparently, scallops will sometimes turn blue on their own under the right conditions.

The colour of the food very much depends on its pH (acidity). I remember learning about this in a biochemistry lecture about 35 years ago and then demonstrating it whilst cooking - adding cream to blackberries. The cream changed the acidity of the blackberries, whose colour changed from purple to blue.

A very good way to achieve a deep green colour would be adding spirulina powder, or possibly barley grass and wheat grass powder.

Blueberries will give a nice purplish hue. Also beets will give a strong red color for natural food coloring.

In order to dye the scallops BLUE, bring RED cabbage and/or PURPLE potatoes to a boil in a pot of water. Tweak the cabbage/potato to water ratio as needed in order to achieve desired pigment (I recommend adding only just enough water for the cabbage and/or potatoes to fit comfortably in the pot). Let the BLUE water cool down to room temperature (be sure to wait long enough as to not cook the scallops prematurely); then, gently plop the scallops into the color bath and place in the refrigerator. Allow 2-3 hours for the dye to sufficiently imbue the scallops.

In order to dye the scallops GREEN, bring fresh spinach and water to a boil. Add only enough water to just barely submerge the spinach. Let the GREEN water cool down to room temperature. Gently plop the scallops in the color bath and place in refrigerator. Allow 2-3 hours for the dye to sufficiently imbue the scallops.

Its a well known fact vanilla ice cream are green in colour. For getting the green colour, you can use vanilla or its products which render green. There are plenty of manufacturers who sell natural green colorant.

regarding blue colour, i am not sure. I think one can try blue grapes to get blue (more of purple) colour.

Apart from this there are lots of green / blue flowers / fruits in nature. Just google it and may get some positive results for colour extraction from the selected flower / fruit. and can be extracted in backyard and can use it.

I dont think spices can render green / blue colour.