How can I make a color changing brick?

To change the color of a BasePart, you need to set its BrickColorusing the BrickColor.new() constructor or its Color using the Color3.new() constructor.

To make the color loop, all you need to do is to make a while true do loop, which will repeat indefinitely.

You also can put tile into a variable so you don't need to repeat yourself too many times.

local tile = workspace.tile

while true do
    tile.BrickColor = BrickColor.new(255,0,0)
    wait(1)
    tile.BrickColor = BrickColor.new(0,255,0)
    wait(1)
    tile.BrickColor = BrickColor.new(0,0,255)
    wait(1)
end