A tweak to snb's conditional format to:
=OR(B3=MIN(IF(B$3:B$20>0,B$3:B$20,9E+99)),B2=MIN(IF(B$3:B$20>0,B$3:B$20,9E+99)),B1=MIN(IF(B$3:B$20>0,B$3:B$20,9E+99)))
will handle zeroes.