I will first talk about colour and inform you what i mean. By colour i mean that all the background on the HCI must be relevant to the colour scheme of the home page and logo. For instance Microsoft's colour is blue and most of there backgrounds and toolbars are blue. So if your logo is green you should make your desktop and toolbars be green. This will make it easier for the user to get use to it.
I will now talk about pattern and let you know what i mean by this. By pattern i mean that all the programs should be layed out the same e.g. were the toolbar is located. For example all of the Microsoft programs all have the toolbars at the top of the screen. So if you want the toolbars to be located of the left or bottom make sure it is all aligned were you want it. All I'm saying by this is that you must make sure the HCI has a template so that users can find the toolbar and tools when they need it.