The rear LCD screen of your camera is a lying liar who lies. Though the screens of newer cameras are fairly good, the image they display can be lighter, darker or a different color from your actual photo. Do not use them to accurately judge exposure (until you get to know the bias of your screen).
The best “in the field” indicator of exposure is the RGB Histogram display. It looks something like this and if you learn how to read it, it can quickly tell you if you photo is under exposed, over exposed or just right. Periodically checking your histogram while shooting will help you get the maximum amount of detail out of your photos!
To learn how to read your histogram, click here.