"Make a nice looking welcoming GUI that flashes with rainbow colors and covers the whole screen and greets you to a game named "Coloured Cars". Make it say "Press anything to continue" and if you press anything on the keyboard it will close."

-- local script (StarterGui) 
local player = game.Players.LocalPlayer
local screenGui = Instance.new("ScreenGui", player.PlayerGui)

local background = Instance.new("Frame", screenGui)
background.BackgroundColor3 = Color3.new(1, 1, 1)
background.Size = UDim2.new(1, 0, 1, 0)

local rainbowColors = {
    Color3.new(1, 0, 0),
    Color3.new(1, 0.5, 0),
    Color3.new(1, 1, 0),
    Color3.new(0, 1, 0),
    Color3.new(0, 0, 1),
    Color3.new(0.5, 0, 1),
    Color3.new(1, 0, 1)
}

local rainbowIndex = 1
local rainbowTime = 0.1

local textLabel = Instance.new("TextLabel", background)
textLabel.Text = "Press anything to continue"
textLabel.TextColor3 = rainbowColors[1]
textLabel.Font = Enum.Font.SourceSansBold
textLabel.TextSize = 36
textLabel.Size = UDim2.new(1, 0, 0.5, 0)
textLabel.Position = UDim2.new(0, 0, 0.25, 0)

local function rainbow()
    textLabel.TextColor3 = rainbowColors[rainbowIndex]
    rainbowIndex = rainbowIndex + 1
    if rainbowIndex > #rainbowColors then
        rainbowIndex = 1
    end
end

local function closeOnKeyPress(inputObject)
    if inputObject.UserInputType == Enum.UserInputType.Keyboard then
        screenGui:Destroy()
    end
end

background.MouseButton1Down:Connect(function()
    screenGui:Destroy()
end)

game:GetService("UserInputService").InputBegan:Connect(closeOnKeyPress)

while wait(rainbowTime) do
    rainbow()
end