The OP may have been referring to Annamarie Tadlock's Honors Thesis titled "Ink Spots as an Indicator of Homozygosity in Tobiano Paint Horses" that was posted to the University of Oregon website on 13 June 2012.
The conclusion reached (in this small study of 66 horses) was that horses with 5 or more inkspots were homozygous for pinto coloring.
Yes, it's a small study. It's also now a moot point, as color testing for pinto variants has advanced beyond the need to guess.
vgl.ucdavis.edu
Above is the link to the current white pattern panel testing available through UC-Davis. Who'd have thought, 20 years ago, that there were so many gene variants that affect white coat patterns?

