In view of the above, 1 with eight delocalised  electrons (Fig. ) similar to 1-methylindene should at a bare minimum, in theory, though not of necessity, absorb blue light ( max ~ 430 -480 nm). However, as reasoned above, the implied conjugative effect lowers the energy gaps between its ungeraden and geraden molecular orbitals such that the  orbitals would be in a much closer proximity to the non-bonding orbitals that accommodate more than twice as much electrons as that in the  bonding orbitals. At this point, in practice, the fundamental electronic excitation of 1 responsible for its orangish colour ( max ~ 480 -490 nm) 10 must be probably, almost entirely due to one of the allowed n u →  g excitations with the highest transition probability, which would not be the case in the absence of its extended conjugation, and as purported in the literature (loc. cit.) would have been of a yellow colour.