Why does the C-Gear flash red or green sometimes

One thing I've always found is that if Bulbapedia doesn't have it, Serebii.net usually does. In fact, they have a page on White Forest/Black City that describes a kinda cheap mechanic: if you play the game, a variable that indicates the "level" of the area will decrease by 3, until it reaches 0. As it decreases, people, trees, and grass will disappear. The only way to stop it from decreasing is to go to White Forest and talk to EVERYBODY, except the nurses and clerks. Keep in mind, this will only stop the process, not reverse it. The only way to reverse it is by using the Entralink to recruit people from Black version. If you need a more in-depth description/walkthrough of the process, go to serebii.net and click "Enter." From there, go to the left navigation bar, find Black/White, and click it. After the page loads, go to the RIGHT side bar, and find the page on Black City/White Forest, it will have all the info I provided and more. I hope that helped!

The day in-game is the same as the current real-world day of the week, assuming your system clock is set properly on your DS.