Still deliberating on the sprites, but I have several possibilities lined up:
Option A - Use the "sonic lemminas" (sprite C in the OP) as regulars and have their tunics be slightly darker for athletes. Zombie and neutral lemminas will remain the same as in the first
Lemminas pack.
Pro: New look for a new pack
Con: Players have to get used to a new colour scheme
Con: I'll either have to tie this theme to each style or create these as new sprites, both of which are options I don't really like
Option B - Use the original lemminas (sprite A in the OP), keeping everything the same as in the first pack.
Pro: Keeps everything familiar
Pro: Further establishes the identity of the Lemminas
Pro: No work required
Con: No new look for a new pack
Option C - Use a totally different coloured set for each level theme. Zombie and neutral lemminas will remain the same as in the first
Lemminas pack.
Pro: Takes "new look for a new pack" to another level
Pro: Gives each new style/theme totally its own identity
Con: Too much like
Lemmings 2: The TribesCon: Players have to get used to
several new colour schemes
Con: More work (although I'm using theme.nxtm for recolouring, so it's not
that much more work)
Con: Ties each theme to the style, which I'd rather not do
Meanwhile, I've now completed at least draft versions of all 50 levels, and 3 of the 5 new tunes are basically finished. There's still a ways to go before it's "demo ready", but it's all coming along nicely

Here's a sneak peek of one of the new tiles. It's an exit for the new "honey" style:
