import arcpy
import pandas as pd
import numpy as np

raster = r"X:RGBraster3.tif" #Change
out_excel = r"X:RGBexcel.xlsx" #Change

arr = arcpy.RasterToNumPyArray(raster)

with pd.ExcelWriter(out_excel) as writer:
    for colorband in range(3):
        df = pd.DataFrame(arr[colorband])
        df.to_excel(writer,sheet_name='Band_{0}'.format(colorband), header=False, index=False)