The chromosome browser on GEDmatch is a little different than the one at FamilyTreeDNA (for those of you who have seen those results). In the graphical results, each color represents a different length of cM (centimorgan, a unit of measurement of DNA). A user should look for red, orange and yellow (and maybe green) when scanning through the browser results. (You can also just look at the numerical results.)
When the GEDmatch user selects two or more DNA test results and compares them in the chromosome browser, the user sees numbers which represent where along the chromosome (and for how long) the match is.
The following image shows just one chromosome - the table with the numbers and the graphical chart - showing where on Chromosome 6 my husband's second cousin GS matches my father-in-law (HH), my husband (SH), and my mother-in-law (AH).
You might be asking: My mother-in-law? I thought this was a second cousin on your father-in-law's side?
Yes, this is endogamy: those of Eastern European Ashkenazi Jewish ancestry descend from a relatively small gene pool.
The yellow segments are likely Handler DNA: The top row is about 47 cM of DNA, part of which (about 21 cM) HH passed down to SH, based on what matches second cousin GS.
All the other little pink and blue segments are just DNA that is likely going to be found in many people of Eastern European Ashkenazi Jewish ancestry, which is why genetic genealogists generally ignore DNA segments less than 7 cM (and often less than 10-15 cM).
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