Top down approach

The task:
Make a function to fade from the current bgColor to a new user-specified colour.

Sub task:
Get user input
Sub task:
Fade from current colour to new colour

Sub task:
Convert current bgColor to decimal
Sub task:
Calculate steps between current colour and new colour
Sub task:
Fade from old to new colours

Sub task:
Extract individual RGB values from hex number
Sub task:
Convert from hex to decimal
Sub task:
Calculate difference between old and new RGB values
Sub task:
Find minimum difference that is != 0
Sub task:
Calculate total number of steps to new colour, and individual increments.
Sub task:
Convert values from decimal to hex notation
Sub task:
Assign each value to document.bgColor property