So after being told by Phil, and talking to my family about it they reminded me of my earlier references "Osmosis Jones" and "How my body works" in order to see how they were able to tackle it.
My father said that the inside of the body shouldn't all be one colour because it isn't, and that I should add a "sky". When re watching Osmosis Jones I realise what he meant by that.
I've been tacking screenshots from the movie as a reference for colour tone and appearance.
By looking at these I realise that I have to draw my texture, I cannot just use an image of the internet.
I want to use Osmosis Jones style in surroundings, by being interesting yet simple.
(I have just seen the post by Simon and he confirms my new take on this, by using hand drawn textures and surroundings which does not take away from the narrative.)