Chemistry Forum

A conjugated system is one in which the single and multiple bonds alternate. The 1, 3 - dienes ring, which has alternate single and double bonds, is an example of a conjugated system. I do know that the ground and excited states of electrons in molecules with conjugated electron systems are closer in energy than in non-conjugated systems. This suggests that lower-energy light is required to excite electrons in conjugated systems, implying that conjugated systems absorb lower-energy light.
The real energy difference between the ground and excited states is determined by the degree of conjugation.

The appearance of a colour of something is the opposit colour of the light what will be absorbed. Blue colour means red to yellow light will be absorbed and vise versa. So blue colour has more conjugation for this reason and vise versa.