Means the same as the phrase baby poop brown.
Some cars & trucks have this hideous brown paint job which has the color of baby shit; hence the phrase, "baby shit brown". This paint job is so old that it is often somewhat faded and has a matte finish (vs. a glossy finish as is usual for automotive paint jobs).

A 1970 Ford Maverick that I had in 1986 sported this type of paint -- faded, matte finish, and colored baby shit brown.
{From a website that has these phoney bologna fake "battles" between TV commercial mascots}:

Parked on the street are a 1986 Honda Accord sporting a dull baby shit brown paint finish (the doors are locked but the keys are still in the ignition) and (again with the keys already in the ignition) a 2014 Kia Soul with a custom lime green paint job.
by Telephony October 26, 2013
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A colour that is inexplicably the shade of a baby's fresh-laid shitstain. Not quite milk-chocolate brown, but light greyish brown with an iridescent tinge of green. The BIC lighter you never want to have.
I went to sit on Andy's bed and saw skidmarks that were baby shit brown.
by pHarmer51 July 16, 2010
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