Final answer:
In conjugated compounds, increased conjugation leads to a deeper color due to smaller HOMO-LUMO energy gaps allowing absorption in the visible spectrum.
Step-by-step explanation:
When observing conjugated compounds in UV and visible regions of the electromagnetic spectrum, a more highly conjugated molecule will have a deeper color. This is because molecules with extended pi systems have smaller HOMO-LUMO energy gaps, meaning they can absorb light in the visible spectrum. For instance, a compound with a system of 11 conjugated double bonds like beta-carotene absorbs light in the blue region of the spectrum, allowing the transmission of light in the red-yellow region, which is why carrots appear orange.
Moreover, the color we see from these compounds is the result of reflected or transmitted light, which is the complement of the absorbed light. Thus, if a compound absorbs light predominantly in the green region of the spectrum, it will appear red because red is the complementary color to green. The degree of visible light absorption and hence the perceived color intensity increases with increasing conjugation.