You think the birch textures is ugly?
This resource pack is what you need!
It replace the texture of birch leaves, logs and sablings with the oak texture. The normal minecraft forest looks way cleaner now.
There is a Server version (also for single player) of this as a datapack.
Currently it's impossible to change the color of the leaves through datapacks, so it's always the same (e.g. in the seasons datapack, the birch leave colors won't change).