"The differences between these two species are subtle, but they definitely exist. I quote from Rudman’s comments in 2001 on his Sea Slug Forum (http://www.seaslugforum.net/find/noumsubn):
“The most important external features distinguishing Noumea subnivalis are the scattered pointed papillae on the mantle and the colour band around the mantle margin. Rather than being two distinct bands, there is a single irregular band which gradually changes in colour from red, on the outside, to orange-yellow on the inside. By contrast, Chromodois verrieri has a completely smooth mantle and there are two distinct colour bands at mantle edge: outer band red, inner band yellow.”
I am able to make out the papillae on the mantle, so I identified the specimen in this photo as Noumea subnivalis."