The short answer is the one most people are not told: the orange comes from added food colouring, not from the tea leaves, not from the spices, and not from the condensed milk.
What is actually in the mix
Commercial Thai tea mix — the stuff in the tall foil bags sold for making cha yen — is typically finely ground black tea plus flavourings and a colouring. The colouring is usually Sunset Yellow FCF (also listed as E110, FD&C Yellow No. 6). Some brands add a little food-grade colouring described simply as “artificial colour” on the label.
Brewed strong black tea is reddish-brown. Add evaporated or condensed milk to that and you get a dull beige. The famous vivid orange of Thai iced tea is a deliberate visual signature, and it is added.
Is that a problem?
That depends entirely on what you want, and it is not our place to tell you. What we can say factually: Sunset Yellow FCF is a permitted food additive in many countries including the UK, the EU and the US, but it is regulated — in the EU and UK, foods containing it must carry a warning label about possible effects on activity and attention in children. Several manufacturers reformulated to avoid that labelling requirement.
Plenty of people drink it happily and it is a genuinely delicious drink. Others would simply rather know what is making their tea orange. Both positions are reasonable; the information just is not usually offered.
What Thai tea looks like without it
This is the part worth knowing: most tea drunk in Thailand is not orange at all. The bright cha yen is one specific street drink, not the national default. Everyday Thai infusions look like what they are:
- Pandan — pale gold, sweet and grassy
- Roselle — deep crimson, and that colour is entirely the flower
- Butterfly pea — vivid blue, turning violet-pink with a squeeze of lime, all of it a real pH reaction rather than a dye
- Chrysanthemum — clear gold, drunk iced across the country
Butterfly pea is the interesting counter-example: a Thai drink that is spectacularly coloured with nothing added at all.
Making cha yen without the colouring
You can. Brew strong black tea (a robust Assam-style leaf works), add a little star anise, a crushed cardamom pod and a small piece of vanilla if you like, sweeten it, and finish with evaporated milk. It will taste like Thai iced tea and look like milky brown tea. Everything people love about the drink survives; only the neon colour does not.
We do not sell black tea, so this is not a pitch — just the answer to the question.