Tom,
Generally if there is no number or letter on the roulette chips the color of the center inlay would be different for each table. The outer rim colors would be used to designate different players on the same table.
In roulette when they pay out a winner, the dealer looks at the rim color if several players are on the same number. When they are figuring out the payoff the dealer will re-stack all the chips by the outer rim color and offset them so they know how many chips each player has bet on the number. If they used the center inlays to figure out who had which chips on a number the dealer would have to take all the chips off a number and stack them out on the layout to see the different inlay colors. I have never seem them do this in all my years of playing roulette.
I hope you understand my explanation and reasoning.
Take care,
"Mr. Roulette"