Before, When I was using a light color theme: blue, white and gray. I got higher earnings But now I'm using a dark theme. Black and Blue, my earnings are drop
Yes, the earnings will drop. It using heavy themes you make the website loading time more. Use a light theme with a white background which is the best. And match the text of ads to your website text. It will help get you more clicks.
Keep testing, testing, testing. Different themes and colors will give you different results. But always have your visitor experience in mind and never break TOS
Sorry to say but I think you just answered your own question. You said when you tested the lighter colors you had higher earnings...so your testing shows you that the lighter colors work better. Why not just go back to using them if that is the results. Sometimes the answers to questions are easier then you think. Sabrina
This is the one that i'm not so sure: Which is better? Same font color ? Or font color are contrary? (like ads=yellow/orange and page=black)
Use a simple theme with quick load time and place the ads in regions where they could be seen by your visitors easily. Never be tricky with ads to make them clicked by your visitors accidentally, it can lead your account to be banned by Google.