Thanks for the reply, yep similar to that.
For the sake of a resolved forum post I went for:
{if $c.categoryid eq 286}rep-sub-cat{/if}
in the end which works fine.
This sits within the existing:
<a href="home.php?cat={$catid}" class="{if $config.Flyout_Menus.icons_icons_in_categories gte $level+1}icon-link{/if}{if $config.Flyout_Menus.icons_disable_subcat_triangle eq 'Y' and $c.subcategory_count gt 0} sub-link{/if}{if $config.Flyout_Menus.icons_empty_category_vis eq 'Y' and not $c.childs and not $c.product_count} empty-link{/if}{if $config.Flyout_Menus.icons_nowrap_category ne 'Y'} nowrap-link{/if}">
in the flyout menus module template:
/common_files/modules/Flyout_Menus/Icons/fancy_subcategories.tplif images are switched off in flyout menus module configurations.