It takes a while but you can learn to see it even though you're looking ahead and it's off to the right.
Astronomers use this trick when they're looking for very faint objects in the night skies, it's called "averted vision" and once you start using it you'll see that it's very easy to pick up the clues that you're looking for, I mean, you really don't need the number, you might be looking for the band to change to yellow or red or be holding out for the gear number to turn red, especially if you're headed up a hill, but there's no "specific" information that you need from the tach. Well, you might want specifically, the speed at the end of a long straight to check gearing but you can actually LOOK for that at the end of your last lap.
Ultimately, you'll be doing enough laps that you find a rhythm in your lap and you'll be shifting at specific places around the track. These spots you will know and remember. You will probably end up having several "option" shift points because you seldom do the same caliber of lap each time round.The color changes that you see coming from the tach will just be confirming what you already know. The road is much more important, no one watches the tach!
