Altering the messenger’s coloration just isn’t doable. Messengers are functions that enable customers to speak with one another, they usually sometimes have a default coloration scheme that can not be modified.
The colour scheme of a messenger is often chosen by the builders of the app, and it’s typically designed to match the general branding of the app. For instance, the Messenger app from Fb has a blue coloration scheme, which matches the colour of the Fb emblem.