The colors might be repeating because the no of dimensions in your dataset is more than the no of colors available in the color palette. You can define your own color palette for your dataset and you can use the same to avoid repetitive colors for the dimensions. To define your own color palette refer to the link below
Swarnalatha Mannar Mannan
Thanks for the reply Swarnalatha.
I have created the custom palette with 20 Colors.
But it is not taking custom palette. By Default it is taking Tableau Medium Palette which is having 10 colors only.