How do I smoothly run through all of the colours?

I made a script which can smoothly go from one colour to another and display it with parts.

https://gyazo.com/17813170705c174b97cf7862459f357f

wait(1)

local group = Instance.new("Model", workspace)
group.Name = "gradient"

local start = Color3.new(0,0,0)
local End = Color3.new(0,1,0)

local size = 100

for x=1, size, 1 do
	wait()
	for y=1, size, 1 do
		local point = Instance.new("Part")
		point.Anchored = true
		point.Size = Vector3.new(.1,.1,.1)
		point.Position = Vector3.new(x/10, 1, y/10)
		point.Color = start:lerp(End, x/size)
		point.CanCollide = false
		point.Name = (x .. ":" .. y)
		point.Parent = group
	end
end

How can I make this smoothly go through all the colours of the rainbow rather than just 2 colours?

Use Tweens on the color value. Here's an example that goes from white to black:

local TweenService = game:GetService("TweenService")
local part = script.Parent
 
local openGoal = {}
openGoal.Color = Color3.fromRGB(0,0,0) -- change this to ending RGB value (black in this case)

local closeGoal = {}
closeGoal.Color = Color3.fromRGB(255,255,255) -- change this to starting RGB value (white in this case

 
local tweenInfo = TweenInfo.new(4) -- how long the tween will last in seconds
 
local open = TweenService:Create(part, tweenInfo, openGoal)
local close = TweenService:Create(part, tweenInfo, closeGoal)


function onClicked()
	if part.Color == Color3.fromRGB(255,255,255) then
		open:Play()
	end
	if part.Color == Color3.fromRGB(0,0,0) then
		close:Play()
	end
end
script.Parent.ClickDetector.MouseClick:connect(onClicked)