I am hoping you have prepared yourself for this tutorial by reading the first page, if not go back and read it!
I am going to use a boy's rez code to change the eye colours of, so we searched for wb.lnz, scroll down until you find [Outline Color Override] this is where we change the eye colour.
The bits with blue boxes are the ones you change. You can find a nice colour by using Carolyn's Colour Chart
If you want to be really special and have two different colour eyes like little here, you change the ones with a blue border to one colour and the ones with red to another.
Let's have a look at what you have done by picking a code from Small & Pampered (make sure it is a baby that matches to the type you are hexing), save the Hex Workshop, say no that you do not want to make a Back Up and then open babyz and enter the code. If it doesn't work first time, try a different code.