Hi Claire you may want to use a limited palette but instead having black&white + one colour you may change the grey scale to another colour, the whole thing will look more full colour rendering. I use -selective colour- in Image adjustment and pick Black in roll down menu , adjust it more green(in this sample here). Then I did the same with Grey. May need desaturate a little the Green in Image at the end.
About the small figure, don't forget the lesson about using the clear silhouette for better eye reading. especially for this tiny figure . the light in the front of the spider should not as strong as the torch.
One more thing,
in Selective colour, you can choose White in drop down menu and adjust it to more blue.