It looks like BD1899 set up an entire Excel spreadsheet to generate a completely randomized NBA roster - appearance, statistics and all. That's actually pretty awesome, and I'll have to try out that roster sometime.
My tutorial will show what I did in this topic (making the rookies NBA 2K14 generates a little more diverse).
It will also show how to make the ones 2K14 already generated in a MyPlayer/Association/season more diverse by copying and pasting values from a spreadsheet I made. To do the latter, the user will need to make a filter in RED MC that only lists generated players, which I cover in my tutorial.
Some of the calculations have logic, like there only being a 5% chance of having ripped muscles or 10% chance of having a right forearm tattoo.
Here's what my spreadsheet looks like:

The CAP_Hcol area has all 0s, since the user has to copy the generated players' original (2K) CAP_Hcol values to my spreadsheet. That way, it can calculate new ones using logic.
If the player's hair color is black (0), a new value won't be calculated for it. Otherwise, it randomly assigns 1-8 (normal hair colors) to to the New column. The Rare column is the same as the New column, but with the rainbow hair colors assigned to a small percentage of players. This will also be explained in the tutorial.