Although I can offer no explaination as to why Atari would decide to produce its Atari 2600jr. in a white case.   Speculation could be that Atari may have been looking into alternative color schemes for the unit or perhaps someone in the production labs was toying around one day and had a case molded in Atari TT white.    After examining the insides of the unit there are no differences whatsoever.   It appears that the only difference is cosmetic.   Weird huh?    It should be noted that the original run of Atari 2600jr's that were made by Atari, Inc under Warner Communications in 1983,  prior to the Trameils taking over has an aluminum lable with small lettering "Atari 2600" in the center of the label with a rainbow bar about 2" long underneath the Atari 2600 lettering inside a raised border of aluminum.    The batch of 2600jr's by Atari Corp under the Tramiels have a long rainbow bar as seen below.