Ruth - you should start using some colour to get moods building in your cities ! A range of lights and darks to evoke if this place is moody, modern, what type of atmosphere etc. It could have a surreal purple sky or a cold grey akin to England and we'd never know! As they're only thumbnails at this stage, they don't have to be flooded with every colour in the rainbow - just enough to show us what you're trying to get across with what stands out in each city descrption to you. This artist does a great job of using colour minimally whilst retaining an intense mood, check his work out!: https://www.artstation.com/artwork/LaeZPIf you have any questions totally feel free to ask !