I've had two of these and changed the batteries once after 1 year and 4000+. Neither screen was "dark". (Now working on 6500 miles.) The LCD faded on one unit when the batteries got low BUT I would not describe it as dark.
I have been very pleased with the simplicity and durability of these units. I hope you did not get a bad one. I would contact cateye and or my retailer for an exchange.