The human eye responds differently to different wavelengths of light (most sensitive to yellow + green if I remember) so the actual shades that Sswift chose to test with could make a difference. Banding will appear in some parts of the blue spectrum more noticably than in others.
As alluded to by Sean, the colour gamut of the monitor will also have a bearing here - the phosphors in a CRT will have a differnet response curve to the light source in a TFT. When asked to display a marginally different shade of blue there might not be a linear jump in hue at all RGB triplets, leading to a perceivable difference (i.e. banding)
As alluded to by Sean, the colour gamut of the monitor will also have a bearing here - the phosphors in a CRT will have a differnet response curve to the light source in a TFT. When asked to display a marginally different shade of blue there might not be a linear jump in hue at all RGB triplets, leading to a perceivable difference (i.e. banding)