Previous experiments address the intergroup bias in decision making, measuring differences between decisions towards in-group and out-group agents. However, we can find contexts in which the group identity of some agents is unknown. This makes it important to study decision making towards this third set of existent agents whose group identity is not visible. Through studying behavior in a coordination game that includes interaction decision making, this experiment addresses the intergroup bias on interaction preferences, including agents whose group identity group remains unknown, and its dependence on the group identity sense saliency. Results show that in the weak group identity sense environment, in-group favouritism and out-group derogation discrimination patterns emerge. Agents exhibit preferences for interacting with other agents that belong to the same group identity group, and provide middle and low effort levels in the coordination context. Furthermore, also in the weak group identity sense environment, a negative discrimination for not interacting with agents whose group identity is not known emerge, and affects not only agents that provide middle and low effort levels in the coordination context, but it even affects agents that provide high effort levels in the coordination context. These positive and negative discrimination patterns in the weak group identity senses environment almost cancel out each other and make the total welfare reached in the coordination context to be only slightly lower than in the environment in which economic agents had not been instilled any group identity sense. We also found that when the instilled group identity sense is enhanced using a group-solving task, agents’ initial in-group favouritism on interaction preferences is similar than in the environment of weak group identity sense. However, initial willingness to coordinate at high effort levels in the coordination context is much higher in the strong group identity sense environment. We show that the higher initial willingness to coordinate at high effort levels in the strong group identity sense environment makes the initial in-group favouritism on interaction preferences to disappear, and leads to higher frequencies of interactions between own, other and unknown group identity agents. As a consequence of these higher interaction frequencies, and the higher willingness to coordinate at high effort levels in the coordination game, total welfare levels reached in the strong group identity sense environment more than doubling total welfare levels reached in both, weak group identity sense environment and the environment without group identities.