setMatrixAt( index, matrix ) {

		matrix.toArray( this.instanceMatrix.array, index * 16 );

	}
Sets the given local transformation matrix to the defined instance. Make sure you set the `needsUpdate` flag of
{@link InstancedMesh#instanceMatrix} to `true` after updating all the colors.

@param {number} index - The instance index.
@param {Matrix4} matrix - The local transformation.