Randomly selecting a block to add more red to?

    Tiles = Instance.new("Model")
    Tiles.Parent = game.Workspace
    Tiles.Name = "Tiles"
    local red = 0

for i=1,30, 1 do
    Brick = Instance.new("Part")
    Brick.Name = i
    brickArray = {}
    table.insert(brickArray, i)
    Brick.Parent = game.workspace.Tiles
    Brick.Anchored = true
    Brick.Size = Brick.Size + Vector3.new(20,0,22)
    Brick.Color = Color3.fromRGB(0,0,0)
    Brick.Locked = false
    if i < 6 then
        Brick.CFrame = CFrame.new(24*i,0,0)
        elseif i < 12 then
        Brick.CFrame = CFrame.new(24*(i-6),0,24)
        elseif i < 18 then
        Brick.CFrame = CFrame.new(24*(i-12),0,48)
        elseif i < 24 then
        Brick.CFrame = CFrame.new(24*(i-18),0,72)
        elseif i < 30 then
        Brick.CFrame = CFrame.new(24*(i-24),0,96)
    end
    print(brickArray[1])
end
local blocks = 30
local Parent = game.Workspace.Tiles --- Here you write where all the tiles are
local children = Parent:GetChildren()


for i = 0,30 do
    for i,v in pairs(children) do --- A script that goes through all the children of your parent
                v.Touched:connect(function()
                red = v.Color.r * 255
                v.Color = Color3.fromRGB(red + 2, 0)
                    if red >= 220 then
                        v.Anchored = false
                        blocks = blocks - 1
                    end
                end)
        wait(0.4)
    end
end

I'm trying to make a game where the tiles start off black, and as they are stepped on become more red. So far it works, but I have a couple issues I can't seem to fix. First, the 30th tile seems to not activate at the same time as the others. It takes a few seconds before it registers touched events unlike the other tiles.

And second, and I can't figure out a way to randomly select a block out of the 30 to add extra red to. What I want is for some blocks to randomly get a bit more red around the map, but I can't figure out a way to do this without interrupting the rest of the script. Using a for or while loop takes over the rest of the script, so I can't figure out how to properly implement my idea.