Every artist has there own way to set up a palette, some use the the color wheel system with the complimentary color on the opposite side of the palette, so when the two compliments are mixed it become a neutral blend which can be used for shadows and to tone areas done.

As you will see here mine is not set up that way, just because this is what I did when I first started painting and have never changed, but the colors are still divided into families of color.

When looking at my palette layout don't worry so much about using the exact same color - think in terms of families of color.