Pink dots are resale tickets, which, in other words, are offered for resale by fans. Since these fans can determine a new price themselves, it may happen that the price differs from other resale tickets or from regular tickets.
Blue dots are regular, primary tickets. These tickets have a fixed price, by the event organization.
It is also possible that you see dark blue dots (these are Official Platinum Tickets) or yellow dots (these are VIP packages). For these types of tickets the price differs as well from both regular or resale tickets.