Resetting PowerShell console colour after running badly-behaved programs
Some programs write their output in different colours. If they're badly-behaved and don't reset the colours when they've finished, your PowerShell console might be left with the wrong background or foreground colours.
This is particularly problematic, because you can't use $HOST.UI.RawUI.BackgroundColor with anything other than the built-in PowerShell colours (which don't match the background used by the default PowerShell shortcut).
The solution is to put [Console]::ResetColor() at the top of your custom prompt function. You do have one of these in your $PROFILE, right?