Problems reported with early iPhone shipments, yellow displays and missing signal barsThis article contains unofficial information.
Apple iPhone 4 Specifications
According to a post on the AppleInsider Forum, the bonding agent used on the iPhone 4 requires evaporation. Apple/Foxconn is shipping the iPhone 4 so fast that the evaporation process is not completed when it arrives at your house. After 1 to 2 days of use, according to the poster, the yellow blotches will disappear.
As far as the phone losing signal strength, reports are coming in all over about the iPhone 4 dropping calls when held left handed, or when the left corner is touched. This could have something to do with the new antenna that wraps around the outside of the phone. When the $29 rubber bumper was placed on the phone, the problem went away. The internet has been inundated with videos showing this problem.
source: InsanelyGreatMac (video), Engadget