Paints are a little tricky to price. Most trade are restockers, meaning they keep the trade up and constantly sell and restock on a particular paint. You have to look into the backpack history to truly tell if they are unsold or not.

For example, take this trade at ~2.3 keys: http://www.tf2outpost.com/trade/23323237

----- On 3/15, there was 21 in stock: http://backpack.tf/profiles/76561198006820530?time=1426402800

----- Today, there are 10 in stock: http://backpack.tf/profiles/76561198006820530?time=1427612400

These paints probably sold slowly over these 2 weeks. I suggest looking at my previous suggestion for this paint to get an idea on how to structure this suggestion: http://backpack.tf/vote/id/54bc3e14b88d88073a8b4959

Like It's Magic said, pricing of paints is not this straight forward, you need to check through inventories of restockers to see if they have sold any, take the previous suggestion for white paint as an example :)