I found an easy and secure way to create custom web apps: using Firefox and the Greasemonkey extension. In Greasemonkey, it's enough to create a user script like this (I've created for Asana):

// ==UserScript==
// @name        Asana
// @namespace   app.asana.com
// @include     https://app.asana.com/*
// @grant       none
// @version     1
// ==/UserScript==

window.Unity = external.getUnityObject(1);

Unity.init({ name: 'Asana',
             domain: 'app.asana.com',
             homepage: 'https://app.asana.com/',
             iconUrl: 'http://asana.com/assets/FluidIcon.png' 
});


This script simply enable the Unity integration, but you can add other features writing more code.

How to create a local webapp userscript
I'm working on a ERP / Accounting (lots of tables and data) web app and was wondering what color scheme would be appropriate for this type of application? Users will be sitting in front of their computers for 8+ hours enetering lots of data on daily basis and I would like to  make that experience as comfortable as possible to their eyes.

Most of these application I've seen are using some sort of a white/grey/blue scheme with white being dominant but I'm concerned that this color might strain their eyes to much especially considering different brightness of monitors and working in the dark. 

Any help would be appreciated.
