Full colour or Duotone?

I feel like my colour choices are still a little messy and all over the place so converting my pages to greyscale, I feel makes it all come together - makes pages look like they belong together and flow better. But keeping it greyscale might look as though I've not really thought about colour and how it interacts with the pages. In the progress surgery, I asked Fred whether I should keep it as it is or do something about it and he suggested that I maybe play around with the monotone and duotone setting for a monochromatic colour effect - so it has colour but more subtle.

Maybe edit the cover as well?

I do like this effect, but now I'm just not sure whether people will think that this is just dull or boring because in the last peer review session, my peer said that she likes the colours because it brings the images to life. I will have to ask for some more opinions..