How do I change the color on a MouseButton1Click event?(edited from previous)

When I equip the tool, the gui pops up and there are text buttons. When I click the text buttons, I want to change the color to red if its green and green if its red, but when I click it the button says " r cannot be assigned to" and that's it.

script.Parent.TextButtona.MouseButton1Click:connect(function()
	if debouncea == false then
	debouncea = true
	a.BackgroundColor3.r = (170)
	a.BackgroundColor3.g = (16)
	a.BackgroundColor3.b = (19)
	elseif debouncea == true then
	debouncea = false
	c.BackgroundColor3.r = (25)
	c.BackgroundColor3.g = (170)
	c.BackgroundColor3.b = (15)
	end
end)

You need to access the Player's GUI, not the game's.

Local Script inside of the tool:

script.Parent.Equipped:connect(function()
	game.Players.LocalPlayer.PlayerGui["Security Tablet"].Frame.Visible = true
end)

script.Parent.Unequipped:connect(function()
	game.Players.LocalPlayer.PlayerGui["Security Tablet"].Frame.Visible = false
end)