Tagged parts not following script

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1

Hello, I am new to scripting and I am trying to make a script where a tagged part has a chance of deleting and has its color changed to one of the three colors.
Thank you for your time.

local CollectionService = game:GetService("CollectionService")
local defaultColor = BrickColor.new(163, 162, 165)
local part = CollectionService:GetTagged("RockColor")
local rockColors = {
	BrickColor.new(107, 122, 145),   -- Red
	BrickColor.new(86, 98, 116),     -- Green
	BrickColor.new(117, 134, 158)    -- Blue
}

local function changeColor(brickColor)
	part.BrickColor = brickColor
end

local function deletePart()
	part:Destroy()
end

for _, part in ipairs(CollectionService:GetTagged("RockColor")) do
	if part.BrickColor == defaultColor then
		local randomChance = math.random()
		if randomChance < 0.5 then
			local randomColor = rockColors[math.random(1, #rockColors)]
			changeColor(randomColor)
		else
			deletePart()
		end
	end
end