Doesn't this do the trick: https://invisioncommunity.com/files/file/7589-group-color-on-user-link/
Alternative try this out, not sure if it still works with the latest 4.2.4/5 version of IPS Community Suite tho:
Step 1:
Go to the theme you want to implement the fix to, and select the HTML Template "userLink"
its found under core > front > global
Step 2:
Replace the entire code in "userLink" with the following below
{{if $member->member_id AND \IPS\Member::loggedIn()->canAccessModule( \IPS\Application\Module::get( 'core', 'members' ) ) }}<a href='{{if $warningRef}}{$member->url()->setQueryString( 'wr', $warningRef )}{{else}}{$member->url()}{{endif}}' data-ipsHover data-ipsHover-target='{$member->url()->setQueryString( array( 'do' => 'hovercard', 'wr' => $warningRef, 'referrer' => urlencode( \IPS\Request::i()->url() ) ) )}' title="{lang="view_user_profile" sprintf="$member->name"}" class="ipsType_break">{$member->group['prefix']|raw}{$member->name}{$member->group['suffix']|raw}</a>{{endif}}
and your done just reload your forum.