The test of a colour note is not whether you can read it. It is whether a stylist who has never met this client can get the same result in eight months while you are on holiday. Almost every note fails that test, and it usually fails for the same three reasons.
Write the formula so it can be re-mixed
Shades, ratios, developer strength and quantities. “6.1 + a bit of ash” is a memory aid, not a record. If you would not hand it to a colourist you have never met and expect the same bowl, it needs more in it.
Record the timing and the starting point
The same formula on different hair at a different starting level is a different colour. What you were working from, how long it processed, and where it was pulling matter as much as what went in the bowl.
Note what you corrected, and why
The most valuable line in any colour record is the one about what went slightly wrong last time and what fixed it. That is the note that stops the same correction being rediscovered from scratch a year later.
Separate what they asked for from what they wear
Clients describe colour in references and feelings — the photo, the season, the word “natural” doing enormous work. Record both the technical result and the human version, because the next conversation starts in the human one.
Keep allergy information separate and current
Allergy and reaction information should not live buried in a paragraph about a fringe. Keep it as its own thing, check it at each visit rather than trusting a note from two years ago, and record patch tests according to your insurer's and manufacturer's requirements — those are professional obligations that no software decides for you.
One habit that makes the rest work
Write the note before the client leaves, not at the end of the day. A note written at six o'clock about a nine-thirty appointment is a reconstruction, and it is the one that ends up saying “usual”. Thirty seconds at the backwash is worth more than five minutes at closing.