What is the difference between a red cummins and a black cummins?

Basically, year of manufacture and what emissions regulations they had to fall under. Pre-2003 ACERT motors are your red tops, whereas Cummins designated their line of diesel motors as a whole new series under the post-2003 regulations (the N14 became the ISX, the M11 became the ISM, the L10 became the ISC, etc.).