Brand colours get chosen on a calibrated screen in a quiet room, and then spend the rest of their life on cheap phone displays, printed cartons, embroidered shirts and photocopied invoices. A palette is only finished when it has survived all of that.
Test it where it will actually live
Before signing off a palette we look at it on an uncalibrated laptop, on a phone at low brightness in daylight, and printed on ordinary paper. Colours that depend on a narrow band of saturation collapse in at least one of those, and you find out in production rather than in review.
Contrast is not a compliance box
Light grey text on white passes a lot of design reviews and fails the moment someone reads it outdoors. Checking contrast ratios early is usually framed as an accessibility requirement, which undersells it — it is also the difference between a brand that reads and one that squints.
Leave room for a second and third tone
A single accent looks decisive in a presentation and runs out of road fast. The moment you need a warning state, a disabled state, or simply two things distinguished on one page, a one-colour brand starts improvising, and improvised colour is what makes an identity look inconsistent.