Basically exactly as the question says, I'm trying to get the background colour out from a website.
At the moment I'm using BeautifulSoup to get the HTML, but it's proving a difficult way of the getting the CSS. Any help would be great!
This is not something you can reliably solve with BeautifulSoup. You need a real browser.
The simplest option would be to use selenium browser automation tool:
from selenium import webdriver
driver = webdriver.Firefox()
driver.get('url')
element = driver.find_element_by_id('myid')
print(element.value_of_css_property('background-color'))