View source for File:MODIS 2007-164-1850 Terra crefl1 721 500m.jpg

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In this composite, MODIS Bands 7, 2, and 1, are assigned to the red, green, and blue portions of the digital image. This combination is most useful for identifying burn scars.

Vegetation and bare ground 
Vegetation is very reflective in the near infrared (Band 2), and absorbent in Band 1 and Band 7. Assigning that band to green means even the smallest hint of vegetation will appear bright green in the image. Naturally bare soil, like a desert, is reflective in all bands used in this image, but more so in the SWIR (Band 7, red) and so soils will often have a pinkish tinge.

Burned areas
If vegetation burns, bare soil in the area will become exposed. Band 1 slightly increases usually, but that may be offset by the presence of black carbon residue. The near infrared (Band 2) will become darker, and Band 7 becomes more reflective. When assigned to red in the image, Band 7 will show burn scars as deep or bright red, depending on the type of vegetation burned, the amount of residue, or the completeness of the burn.

Water
As with the 3-6-7 composite, water will appear black. Sediments in water appear dark blue.

Short Answer
Bands
7,2,1 (2,155 nm: 876 nm: 670 nm)
Colors
Vegetation=Green
Water=Black or dark blue
Desert/Naturally bare soil=Sandy pink
Burn scar=Red to reddish-brown, depending on the nature of the pre-fire vegetation and the severity of the burn.
Advantages
Distinguishing burn scars from naturally low vegetation or bare soil. Enhancing floods.