Transparent

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "name": "Transparent",
  "version": "1.1.2",
  "manifest_version": 2,
  "description": "Changes the background of images on the dash to blue when moused over to make viewing transparent images easier.",
  "icons": {
    "16": "icon_16.png",
    "48": "icon_48.png",
    "128": "icon_128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "http://www.tumblr.com/*",
        "https://www.tumblr.com/*"
      ],
      "css": [
        "main.css"
      ]
    }
  ]
}