Help to find out why vertexColors make small triangles' color is blur(cannot seen clearly)?

When zoomin, please check the red part(contains lots of small triangles 2pixel*2pixel) in the following,

source code:
this.mesh = new THREE.Mesh( undefined, new THREE.MeshBasicMaterial( {
side: THREE.BackSide,
//color: 0xffffff,
vertexColors: true,
} ) );
let geometry = new THREE.BufferGeometry().setFromPoints( vertices );
geometry.index = new THREE.BufferAttribute(indexes, 1);
geometry.setAttribute( ‘color’, new THREE.Float32BufferAttribute( colors, 3 ) );
this.mesh.geometry = geometry;

I’m afraid neither your screenshot nor your code explain the issue clear enough. Probably best to demonstrate the problem with a live example.

Sorry, I add wireframe screenshot
I search forum, my issue maybe related to color gradient or color interpolation.
Similar with Interpolate Vertex Colors in HSL Space
But I do not know how to fix this issue