Mark Sanderson , Oct 18, 2012; 12:13 p.m.
I would just make one up .........there is a risk in that if the color is off, it reflects badly on you when they show their friends/family.
You may want to consider keeping control of that process at least as an option.
Get some samples made from your local Walgreens/Costco/Sams etc......and some from a color corrected pro lab (MPIX, WHCC etc) and show them the difference.
Costco can do a good job if you use their ICC Profiles for your local store, but then you are in control, hard for the customers to do this.