Change
if (checkcolor != "0xFFFFFB")
to
if (checkcolor = "0xFFFFFF")
and see if it works. If not try decresing the CheckBoxX variable one step and reload the script and try again. Hopefully it works without that adjustment, but if it needs it it should work after less than 5 tries.
Edit: "How can I find the color of the checkbox?" forgot that one, see a bit up in this thread, there is a very little mini guide how to find it. The spy tool comes with autohotkey.