Give a different style to `Message` part depending on log level

**Is your feature request related to a problem? Please describe.**

Specifically to give a different color to the `Message` part depending on log level. Why not being able to completely have a style for `Message` depending on log level ?

**Describe the solution you'd like**

A map for `Message` would be breaking change so it's not that good. Maybe we could have a new property ? But it could be ugly in a way of two properties can change the `Message` style ?