Candle
The one that stands in for any of the others — and the reason a beginner needs only one box.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Before anything else about candle colours, the honest caveat: the tables disagree. Agrippa gives a chapter to light, colours, candles and lamps and ranks colours under the planets; later ceremonial magic elaborated on that, and twentieth-century books elaborated again in several incompatible directions. No two widely used lists agree in full, and there is no canonical one hiding somewhere.
White is the exception everybody accepts. It substitutes for any colour in any system, and the reason is at least partly practical: for most of the history of candles, plain tallow or beeswax was simply what you had. Coloured wax is cheap and modern. A practitioner in 1650 working a money charm was not holding a green candle.
So white does clarity, peace, purification and spirit work in its own right, and does everything else by proxy. It is also the sensible thing to buy first. If a book insists a working fails without the correct colour, the book is selling candles.
Readings practitioners have offered, ordered by how many recognise them. Take what serves, leave the rest.
Carried forward
Heinrich Cornelius Agrippa, Three Books of Occult Philosophy (1533)
Agrippa sorts colours under the planets — black to Saturn, red and fiery shades to Mars, green to Venus, white and silver to the Moon — and treats a lamp or candle as a way of putting that planet into a room. The scheme is astrological before it is anything else, which is worth remembering when a modern list gives no reason at all.
Carried forward
Common in contemporary practice
One box of plain white tealights, used for everything, with the colour supplied by a ribbon or a scrap of coloured paper underneath when it matters. Nobody has ever reported worse results.
Credit what you carry. Much of this comes from living traditions, and some of it from traditions that are closed — held by particular peoples and not offered for general use. Where you know whose practice a reading came from, name them; where you don't, say that too.