Lighting problem

in lighting , does the surrounding texture affect the lighting scene ? as soon as i am using textures, the lighting changes, its becoming dark ,why ? I am using a small engine with a robot in it, the robot is made of sphere and cubes, since im using octree, the color of the robot(blue,white and red) changes from one node to another sometimes, and most of the time it appears much darker. When I stop using texture mapping, the robot returns to its original colour and remains that way ,wherever i may roam. Before using octree the robot had its original color though Anyone can help me out Muksitul