Love the way you did the eye! its nice to see someone else on here who is also interested in scientific illustration
thats what I want to do as well!! Would be interested in the species challenge you mentioned if you would be able to post the link?
I have recently been working on a grey cat and had a similar problem of whether to go 100% complementaries to mix the grey fur (there is a really good thread in the library called "African Grey Feather" about this), but I ended up doing a mix of complementaries, plus some greys mixed in.
I found that an undercoat of Ultramarine and Caput Mortuum (a reddish brown colour) both polychromos, with dark indigo on darker areas, then greys, whites and blues over the top worked quite well.
great finished artwork!