Grace ends by removing itself. Legge's translation shows one with white as his only ornament, and grants that there will be no error. A hexagram that has spent five lines on adornment closes on the absence of colour, and the closing is not a rejection of anything that came before it. White is still named as an ornament here. The line does not say that decoration was a mistake; it says that at the summit the last refinement available is to take the decoration away.
The sequence supports the reading. The first line declined a carriage, the fourth arrived in unrelieved white, the fifth gave less than it could have, and the sixth completes the movement by keeping nothing back to display. Each step reduces rather than adds, and the hexagram turns out to have been describing a progressive stripping all along, with the middle lines showing how much is lost when ornament is allowed to lead.
A yang stroke stands in this even position at the top of the upper trigram Gen, past the ruling fifth place and formally incorrect by the letter of the rule. Being outside the ruling seat is what makes the plainness available, since nothing at this height has to be maintained for anyone. The verdict of no error is modest by design. Nothing is gained at this position and nothing is claimed, and the hexagram of beautiful appearances is content to finish with an appearance that asserts nothing at all.