Brick colour change script isn't working?

Events cannot be used as conditions, nor do they act like conditions.

Use a separate function for Touched, such as:

game.Players.PlayerAdded:Connect(function()
    script.Parent.Touched:Connect(function(hit)
        if game.Players:GetPlayerFromCharacter(hit.Parent) then
            if workspace:FindFirstChild("Wall4", true) then
                local wall = workspace:FindFirstChild("Wall4", true)
                wall.CanCollide = true
                wall.BrickColor = BrickColor.new("Really red")
            -- Your other function would go here
            end
        end
    end)
end)

Let me explain why you can't use events in conditional statements.

Events are RBXScriptSignals. RBXScriptSignals are signals that act like triggers for given functions; when they fire, a function is usually associated with it (unless you use Wait()). However, the main reason why they can't be used as conditions is because RBXScriptSignals don't return any values, they simply pass them. The difference is that passing a value means giving it to a function, and returning a value means that a function passes its own value to wherever it is called.

Uh maybe, just maybe this script will help you, the scripts on top is incorrect.

game:WaitForChild("Players").PlayerAdded:Connect(function(plr)
        local stage = plr.leaderstats.Stage
        stage.Changed:Connect(function()
        if stage.Value >= 1 or script.Parent.Touched then
            script.Parent.CanCollide = false
            game.Workspace.Walls.Wall4.CanCollide = true
            game.Workspace.Walls.Wall4.BrickColor = BrickColor.new("Really red")
        end
        end)
        end)

so i can't really read the whole thing but:

game:WaitForChild("Players").PlayerAdded:Connect(function(plr)
    local stage = plr:WaitForChild("leaderstats"):WaitForChild("Stage")
    stage.Changed:Connect(function()
    if stage.Value >= 1 or script.Parent.Touched then 
        script.Parent.CanCollide = false
        game.Workspace.Walls.Wall4.CanCollide = true
        game.Workspace.Walls.Wall4.BrickColor = BrickColor."Really red" --- that might be the problem,you should use . random
    end
    end)
    end)

---make sure its anchored too.