Hi Gene,
I was told that the lightening was done at the club itself by applying a bleach solution to lighten the center of the chip. Weather it was for security reasons or just to make the chip a little more fancy I couldn't tell you. All I do know is that every other chip of this denom and mold I have seen have had the center bleached white. Maybe Armin has an answer and will post it on TCB.
Hava Good One