In 1966, Topps created a new color scheme to identify the cards for each team. One AL and one NL team used each of ten colors, which were found on the card's nameplate and the diagonal banner. The same color scheme was used in the 1968 set and (with the addition of two colors for the four expansion teams) the 1969 set. The circles on the '68 and '69 cards were colored according to the player's team.
In the 1967 set, Topps strayed from that scheme. Although they still had an AL and NL team assigned to each color, the color assignments were shuffled to other teams, except for both "red teams" (Yankees and Dodgers), the Giants, and the Cubs. The team name at the bottom of the card was colored accordingly.
(Topps also replaced gray with light blue for the 1967 set.)
Why were the colors changed in 1967, only to revert back for the 1968 set? Not that I minded; my favorite color at the time was yellow, and my favorite team was the Phillies, so it was all good.