Candle
Cool water and plain truth — the candle for the conversation you have been dreading.
These are associations the community holds, not settled fact — the more a reading is shared, the bolder it sits.
Blue carries peace, truth, healing, sleep and patience across almost every modern list, and the planetary attribution is a muddle — Jupiter in many books, the Moon in others, Neptune in twentieth-century ones written after Neptune was discovered in 1846. That last is a useful reminder that these tables are still being edited, and that anything citing Neptune or Pluto is by definition modern.
The colour itself is doing obvious work. Blue is water and cold air and distance, and it is what people reach for when a situation is too hot. Where red is nerve and yellow is words, blue is the deliberate lowering of temperature that lets either of them be used well.
Practitioners burn it for difficult conversations, for sleep, for chronic rather than acute trouble, and for truth-telling — including the kind aimed at oneself. It is slow. Work started with a blue candle tends to want more than one sitting, and that is generally the point rather than a fault. White substitutes; purple where the work turns inward.
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)
Jupiter in Agrippa is the temperate, expansive and merciful planet, and takes the clear and airy blues. His interest is in proportion: a Jupiterian working is meant to widen a situation rather than force it, which is a fair description of what a calm conversation does.
Carried forward
Common in contemporary practice
Lit before a hard conversation rather than during it, on the grounds that the useful effect is on the person who has to have it. Several practitioners keep one purely for sleep and never use it for anything else.
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.