How can I write Color3 Value in the table?

First of all, instead of having three separate tables, why not just use one? Secondly, why store both BrickColor names and then Color3 values? Here's an easier implementation.

Tables

local spells = {
	{ 
		["name"] = "Avada Kedavra",
		["color"] = "Lime green"
	},
	{
		["name"] = "Duro",
		["color"] = "Bright yellow"
	},
	{ 
		["name"] = "Avada Kedavra",
		["color"] = "Bright red"
	}
}

The CreateSpell bit

for x,y in pairs(spells) do
	if SpellName == v["name"] then  -- Checks if SpellName is the same as the current spell we're on
		Tool.Activated:wait()
		functions.CreateSpell(BrickColor.new(v["color"]),SpellName,Player)
	end 
end 

You'll need to rewrite the CreateSpell function itself a bit to remove the 2nd Color3 argument, and instead make it so that it uses the BrickColor passed to it.