IBM PCjr Manual page 46

We are now going to show you several keys that must
be used with other keys to perform actions. One such
key is the Alternate (Alt) key, and the other is the
Function (Fn) key.
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Press the Alt key. It is the key with
a blue border around it - to the left
of the Space bar.
Did you notice that the screen turned blue? This
happened to show you that any key with a blue stripe
under it can be used with the Alt key to do special
things. (We thought this would be an easy way for yov
to remember them.)
2-30 Getting Started