Being new to scripting, I thought it would be script.Parent.one.Transparency = 0.7
but this didn't seem to work, so I tried script.Parent.one.BackgroundTransparency = 0.7
again, this didn't work so I turned to ROBLOX Wiki, but only found stuff on basic GUI stuff like resizing and positioning.
Your script is actually correct, thanks to ROBLOX. They fix both ROBLOX Studio AND ROBLOX Player every night. Check to make sure that all your items are right location. (Example: the Script and the Text named "one" are both in the same ScreenGui, if that's how you set it up.)