[ARW VISIONS]

Ok so in your .tpl you will find class="bestsellers-products-item-m"

this controls the background color.

you need to code the tpl to change this class based on category.

so in your .tpl you would have

{if $cat eq '8'}
class="bestsellers-products-item-m-blue"
{elseif $cat eq '10'}
class="bestsellers-products-item-m-pink"
{else}
class="bestsellers-products-item-m"
{/if}

then create appropriate class in your CSS