Green colour resulting from the formation of pi complex

Peter Sykes mentions in Guidebook to Mechanism in Organic Chemistry (6th ed.) on p.132 that there would significant differences in physical properties of the resultant mixture when we:


1. React methylbenzene with $\ce {HCl}$ to form a $\sigma$ complex
2. React methylbenzene with $\ce {HCl}$, with $\ce {AlCl3}$ as Lewis acid catalyst, to form a $\pi$ complex


One of the differences he mentioned was that the former would remain colourless while the latter would give a green colour. However, he did not make clear what gives rise to the colour difference. Is it due to formation of the $\pi$ complex?


