Also, your code can (and did!) pick the same square and same color twice in a row! So the user can't see any change.
And you have some problem with the timeout on a new game, as things seem to speed up a lot.
Oh...and the browser converts style.backgroundColor="Blue" to "blue". Chrome does, at least. I vaguely recall the FireFox converts it to RGB. So you really should *NOT* be testing the color of the cell. Instead, just remember it in a variable.
Also, IDs that start with a digit are frowned on. There are circumstances where they won't work.
An optimist sees the glass as half full.
A pessimist sees the glass as half empty.
A realist drinks it no matter how much there is.