Step 1: Recall how an FCC works.
In a standard False Colour Composite the near infrared band is shown as red, the red band as green and the green band as blue.
Step 2: Note the vegetation colour.
Healthy plants reflect strongly in near infrared, so they appear bright red on an FCC; this helps us tell other features apart.
Step 3: Think about rock outcrops.
Bare rock has no strong infrared reflectance like plants and tends to look pale and earthy in colour.
Step 4: Compare the options.
Bright red is vegetation, light blue to white is usually sand or dry soil, and mottled black often means water or shadow, so none of these fit bare rock.
Step 5: Match rock outcrops.
Rock outcrops show up as a light brown signature on a standard FCC.
Step 6: State the answer.
The colour signature is light brown.
\[ \boxed{\text{Light brown}} \]