[o]

Most aromatic compounds appear white, but azulene, and other aromatics, appear with bright colours. Is this simply a direct result of having a long conjugated chain, or are there other factors at play? Is it the fact that the molecular orbitals get closer to each other as more conjugated carbons are added, thus decreasing the energy of the absorption?

[cpncoop]

Several factors are at play here (in fact azulene itself can do some things that no other chromophores are capable of)... but I think the reason is that with increasing conjugation, the energy gap required for absorption of light gets smaller, which means that the transitions shift from the UV into the visible region - which is why we observe colors.  There are other factors at play here as well (fluorescence for example - especially in the case of azulene which can fluoresce from higher triplet levels). but the basic answer is that increased conjugation in fused ring systems leads to the ground and excited energy states being separated by less energy.