Clumping can't give color to each layer

I try to change color for each sphere layer, but it doesn't seems to work. I want to give layer that is divisible by 2 to be brown and layer that isn't divisible by two as white.
--------------------------------------------------The method I tried that doesn't work-----------------------------------------------------------
        # Check if the sphere is within the clump limit
            if abs(xi) <= clumpLimit and abs(yi) <= clumpLimit and math.sqrt(xi**2 + yi**2) <= diameter/2:
                # Move spheres in layers 2, 4, 6, and 8 in x and y axes by 2mm
                if layer % 2:
                    xi += 0.002
                    yi += 0.002
                    color = (1, 1, 1) # white
                else:
                    color = (0.647, 0.165, 0.165) #brown
                sphere_obj = sphere([xi, yi, zi + z_offset], radius_clump)
                # Assign material properties to the sphere
                sphere_obj.material = clump_plate
                # Assign color
                sphere_obj.color = color
                bodyList.append(O.bodies.append(sphere_obj))
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#### My Code ###
import random
import math
from yade import geom, pack, utils, plot, ymport, export
import numpy as np

# Define cylinder with funnel parameters
center = (0, 0, 0)
diameter = 0.102
height = 0.18

# create cylindrical body with radius 0.102 m and height 0.064 m
cylinder = geom.facetCylinder(center=center, radius=diameter/2, height=height, segmentsNumber=80, wallMask=6)

# add cylinder to simulation
O.bodies.append(cylinder)

# plate properties
clump_plate = CohFrictMat(density = 7500, label = 'clump_plate')

# add properties
O.materials.append(clump_plate)

# clumping parameters
bodyList = []
zi = 0.1
radius_clump = 0.00221
clumpLimit = (diameter/2) - 0.005
# layer and offset condition
num_layers = 8
z_offset_increment = 0.00128

for layer in range(num_layers):
    z_offset = layer * z_offset_increment # Adjust the z-coordinate based on the layer

    for xi in range(-50, 51, 4):
        xi = xi / 1000
        for yi in range(-50, 51, 4):
            yi = yi / 1000

        # Check if the sphere is within the clump limit
            if abs(xi) <= clumpLimit and abs(yi) <= clumpLimit and math.sqrt(xi**2 + yi**2) <= diameter/2:
                # Move spheres in layers 2, 4, 6, and 8 in x and y axes by 2mm
                if layer % 2:
                    xi += 0.002
                    yi += 0.002
                sphere_obj = sphere([xi, yi, zi + z_offset], radius_clump)
                # Assign material properties to the sphere
                sphere_obj.material = clump_plate
                bodyList.append(O.bodies.append(sphere_obj))