Specialist Ratchet is based on the colours they were going to use for movie Ratchet before changing their minds and making him green.

A white Ratchet is nothing new, we've had plenty of Rescue Ratchets before.
Legends Rescue Ratchet
Voyager Rescue Ratchet
FAB Rescue Ratchet*
Titanium Series Rescue Ratchet*
Deluxe Rescue Ratchet

Also, you can see "Rescue Ratchet"** in the first Transformers movie - in the scene where Lennox and his men touch down in the U.S. and are intercepted by Sector 7, in the background of their airfield you can see "Rescue Ratchet"
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*not sure if these came out in Australia - I personally don't recall seeing them
**Okay, it's not really Ratchet but rather an identical vehicle to his alt mode in the same colours/deco as Rescue Ratchet! Still, a neat little nod to Ratchet's G1 colours placed in the film.