Why is my Gui only works on Test or Play Solo?

So i made a gui that u can choose a color to change a brick and using String values to change it and adding Changed event to it to sync the color but i also add a Checking and put it inside on the

game.Players["ThePlayer"]

so i'm the only one can do it, it is a BoolValue so if it is true it will run else so on.. so to access the player i need to use Local script to make it easy so it worked well and i'm really proud of myself but i didn't think that when u actually test it on a real game not on Play Solo the gui won't even run the only it can run is Normal scripts inside the gui to make an Tweening effect when opening it but when it comes to local script it won't run? how so? any idea? or is it just a bug?

Hello Angelie. Click on the StarterGUI, You'll probably see a property called ShowDevelopmentGUI unticked, click the checkbox to make your gui appear.