We see an object when the light reflected from that object hits the eye.
When white light from the sun falls on an object, sometimes the object absorbs some parts of the light. The rest of the white light will be reflected off the surface of the object.
If the object reflects all the parts of the light, the object will appear white. If the object absorbs the light completely, its colour will be black.
We see the object in the colour of the light reflected off its surface.