Use IWebElement.GetCssValue
There is a method for getting the computed css style. I believe in c# it is the IWebElement.GetCssValue method.
Note that in the documentation for this method in ruby and java says the following. I assume it applies to c# even though it is not mentioned.
Note that shorthand CSS properties (e.g. background, font, border,
border-top, margin, margin-top, padding, padding-top, list-style,
outline, pause, cue) are not returned, in accordance with the DOM
CSS2 specification - you should directly access the longhand
properties (e.g. background-color) to access the desired values.
Example (ruby)
Since I have only done selenium-webdriver in ruby, I can only give a ruby example (idea is the same though the api is slightly different):
require "selenium-webdriver"
driver = Selenium::WebDriver.for :firefox
driver.navigate.to "http://yourpage.com"
element = driver.find_element(:id, 'id')
puts element.css_value('color')
