Well, in most cases you can't buy less than a 1/4 yard cut (fat or skinny) of a particular fabric, so I would go with that measurement.
So, I'd buy 5 FQ's for the coral color (or whatever color you're substituting if you're not making an exact copy)
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And I'm going to sound like a broken record, but you have to look at the pattern and see how the fabrics/colors relate to each other.
Are the corals pretty much the same value in the quilt? Because if you get a very light one and a very dark one, then that could affect the way the pattern turns out.
If you did buy the 4 or 5 corals (or whatever color) and decided you wanted more, then post a picture of your selection to date, and I will be more than willing to whack off a couple of pieces that would match so you can have a greater selection.
I'm a huge fan of having 30 plus fabrics in a quilt - planned, not scrappy. So, yes, those of us with huge stashes could probably pull out 30 fabrics at a minimum for each color/value request.
But you gotta start somewhere. ;-)
Can you post the name of the pattern, or provide a link to a picture?