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 Datapack/Mod version which changes the worldgen to not gernerate Birch Trees instead of changig the texture.
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).