Welcome to BR
First off, if you're new to topwater fishing, a Spook is a poor choice to start with as it takes a while to learn how to work it. It isn't a cast an crank back type of lure.
That fish can't see the sides of a topwater lure is a myth. They are rarely directly beneath the lure and depending on how the lure is worked, most often the sides are exposed at some point. There are quite a few posts here about lure colors and how important they are. You can do a search and read up if you like.
Depending on the water clarity, any belly color can be productive. The clearer the water, the lighter the bottom color is a fairly good guideline. You can find clear bottoms on some lures, but most of those are clear bodied, or at the least opaque. White and bone are the ones you'll see most often as far as light colors go, but yellow and chartreuse also work under low light conditions. Many of those will have a different color toward the nose of the bait, or spots, but as long as there is a predominate color, let that be your deciding factor when purchasing.
In bass fishing, there are always exceptions and with topwaters, black is the one you'll hear most often. My 2nd most productive color for a Spook is black and I throw it in super clear water under sunny skies.