File:AS12-56C-8392red-AS12-56B-8392blue grain extract.jpg

English: Image created using two Apollo 12 Hasselblad camera frames, with the mountain informally known as Lalande η at center. AS12-56C-8392 had a red filter (660 nm), and AS12-56B-8392 had a blue filter (430 nm), and both were part of the Apollo 12 Multispectral Photography Experiment. This was created in GIMP by aligning the two images and applying the grain extract mode with the blue image on top (difference and subtract modes did not produce the desired effect). This approximately replicates the effect shown in Figure 9-6 of the Apollo 12 Preliminary Science Report (NASA SP-235), which has the following caption:

Contrast-stretched red-minus-blue difference picture of the center portion of frame 8392. Dark areas are bluer and light areas are redder than an arbitrary point taken as neutral gray. The light vertical banding is an artifact introduced in the scanning process. Slight misregistration of the red and blue frames enhances crater boundaries. In addition, color information cannot be obtained from deep shadow areas; hence, those areas will appear anomalously colored.

The text of the report states:

Distinct color differences are evident, in particular between Lalande η and the surrounding mare and between what appears to be secondary-impact ejecta rays and the surrounding mare. Although the frames have not been calibrated for camera vignetting or adjusted to a lunar standard by Earth-based photometry, there is now, for the first time, clear evidence for local small-scale color variations on the lunar surface.