The thing is, L6S Specialist can wear anything, depending on where he is. Here is a good example.
L6S guy #1 works in a shipyard, dealing with mechanics, welders, painters. He wears jeans, long sleeve button up shirt tucked in, hardhat & steel toe boots when in production areas.
L6S guy #2 works for car company in an office, wears chinos, button up shirt tucked in and boat shoes or oxfords.
L6S guy #3 works for Goldman Sachs in NYC and wears a suit.
All three guys are essentially doing the same job, but work in totally different environments. As far as I'm concerned, I'm probably somewhere in between guy #2 and guy #3. If this was an in person interview in their offices, I'd be in a suit. But it's a VTC and I'll be in my house. From the sounds of it, shirt and tie is acceptable. Suit would probably be okay too but I'm really not trying to over think this.