Question

how can we see the colour of non luminous and opaque object

Answer 1

An opaque object is neither transparent nor translucent. The Non- luminous objects are one that reflect the light from the luminous objects.

The color of non-luminous and opaque object depends upon the color of the light reflected by it.

And, the color of the reflected light depends upon the color of the incident light.

Answer 2

Answer:

When light falls on a non- luminous object such as a book, it bounces back in  different directions. When this reflected light reaches our eyes, we are able to see the  object.