From Mannix:
In the 1960s, auto companies typically didn’t give a TV series multiple “star cars” to use, so Mannix (and Barris) had to make do with a single 1968 Dart GTS. “Originally it was a red car, and Bruce Geller said that’s too bright, let’s make it a racing car green. I think this car, underneath, still has some red paint on it,” Connors remembered.
Here's proof it was originally red, all one had to do was wait until the hood got opened for the bad guy to drain the brake fluid and cut the "emergency" or parking (your choice
) cable. Looks like a 340 orange engine not the turquoise 383 ('68) engine color. I always thought it was a 383
