How this match is calculated
Every Dunn-Edwards and Farrow & Ball color in our database is converted to CIELAB coordinates, then scored with the CIEDE2000 formula — the current ISO standard for how different two colors look to the human eye. It corrects for the fact that the eye notices small shifts in some hue ranges far more than others, so it compares digital colors in perceptual space instead of treating RGB channel differences equally.
Stiffkey Blue ranks as the closest Farrow & Ball equivalent to Ragtime Blues because it sits nearest in that perceptual space. This ranking compares stored digital values, not measured paint samples. It is not a physical match or touch-up guarantee. Sheen, lighting, and the existing wall color all shift perceived color, so order a sample of Stiffkey Blue and check it in your actual room before committing.