Changing the theme of a Sharepoint site is an easy task through PowerShell. there are a couple of available themes that you can choose from.

You can use the following themes in WSS 3.0

Beltown
Breeze
Cardinal
Citrus
Claasic
Default Theme
Granite
Jet
Lacquer
Lichen
Obsidian
Petal
Plastic
Reflector
Simple
Verdant
Vintage
Weat

To change Theme, we can use the ApplyTheme() method. Before we use the method we define which site we want to change theme on, In my case, I’ll change it on the TopSite.

PS > [System.Reflection.Assembly]::LoadWithPartialName("Microsoft.SharePoint")

PS > $SPSite = New-Object Microsoft.SharePoint.SPSite("http://wss"); $OpenWeb = $SpSite.OpenWeb(); $OpenWeb.ApplyTheme("Obsidian"); $OpenWeb.Dispose(); $SPSite.Dispose()

If we look at our site through Internet Explorer, we can see the change: