Ruby on Rails change background colour in CSS according to database

In my Ruby on Rails application I am trying to allow the user to choose their colour and have this as the sites background.

In my schema I have this preferences table:

create_table "perferences", force: :cascade do |t|
  t.integer  "user_id"
  t.integer  "category_id"
  t.datetime "created_at",  null: false
  t.datetime "updated_at",  null: false
  t.text     "colour"
end

The CSS background colour is in the following line:

body{line-height:1;height:100%;width:100%;color:#B2BFCB;background:#002952;text-align:center;font-family:"Apercu Regular", Calibri, sans-serif;font-weight:normal;font-style:normal;margin:0;padding:0;}

But I am unsure as to how to update the colour based upon the colour in the database.

I have tried to follow this link: http://ift.tt/19vMCMZ But I got the error: undefined method formatted_colour_path for #<#<Class:0x6daa0a8>:0x6881b98>

In the view:

In the perferences controller:

def show
   @colour = Perference.find_by(user_id: session[:user_id]).colour
   respond_to do |format|
        format.html
        format.css
   end
end

Can someone please help. I understand that I need to retrieve the colour from the database and then use this to update the CSS, but I am not sure how to do this.