About material alpha

My English not so good,I try to be brief .When I set alpha<1,It seemed obvious the color overlay.
My problam is how to make the color don’t overlap

When transparent faces overlap, you won’t get a consistent color. This is the expected result of alpha blending.

Also notice that three.js has problems to handle such transparency setups without artifacts. You might want to consider to model you streets with an opaque color.

If one vertex is behing the other you might be able to prevent the furthest pixel fragment from rendering by using the depth buffer and discarding it.

See my answer on this thread I think you can use the same approach, particularly in relation to depthTest & depthWrite: Transparent faces in Three.js - #4 by becky_rose

It’s a clever way,thank u