Question

why is the forest ground dark in colour

Answer 1

Hey there
The answer is
The sun's rays do not get the space for reaching the Earth's ground
That's why it appears dark

Answer 2

There are different reasons for the dark color of the forest ground.

First of all because of dense canopy overhead sunlight cannot enter the forest and cannot reach the ground.

Furthermore the ground remains covered with damp soil, decaying leaves, shrubs, twigs, and decayed fruits that makes the forest ground blackish in color.

Sometime the presence of humus on the forest ground makes the ground blackish.