In this image dark blue represents low points and yellow represents high points. Thus the blue molecules at the left of the image are adsorbed on the Ag(111) surface while the yellow molecules lie atop the adsorbed layer. Notice how the second layer molecules (yellow) appear homogeneous while light blue and dark blue molecules are visible in the adsorbed layer. In bulk C60 at room temperature, the molecules rotate once every nanosecond, many orders of magnitude faster than the STM images. Thus the bulk-like second layer appears uniform. The interaction with the Ag surface slows the molecular reorientation time to minutes and so different molecular orientations can be observed in STM images of adsorbed C60. For more details see E.I. Altman and R.J. Colton, Surface Science 295 (1993)13 and E.I. Altman and R.J. Colton, Physical Review B 48 (1993) 18244.