These are very interesting and certainly seem to form a pattern. I'll see how many more suggestions come in and then I'll finish my own list and see what you think. Many thanks.
It's a different version of a Best/Worst list, so I'll join in...but ultimately, it's all very subjective.
I tried to use the episode guide, but I'm sure I either missed or duplicated some....but this was a fun exercise.
Green:
Murder by The Book
Death Lends a Hand
Suitable For Framing
The Most Crucial Game
Etude in Black
Any Old Port in a Storm
Swan Song
A Friend in Deed
An Exercise in Fatality
Negative Reaction
By Dawn's Early Light
Playback
Forgotten Lady
Double Exposure
Now You See Him
The Bye Bye Sky High IQ Murder Case
Try and Catch Me
Make Me A Perfect Murder
Columbo Cries Wolf (ABC)
Columbo Goes to College (ABC)
Yellow:
Prescription Murder (pilot)
Ransom for a Dead Man
Dead Weight
The Greenhouse Jungle
Requiem for a Falling Star
A Stitch In Crime
Double Shock
Candidate For Crime
Publish or Perish
Mind Over Mayhem
Troubled Waters
A Deadly State of Mind
Identity Crisis
Fade Into Murder
Old Fashioned Murder
Murder Under Glass
How to Dial A Murder
The Conspirators
Columbo Goes to the Guillotine (ABC)
Murder Smoke And Shadows (ABC)
Sex and the Married Detective (ABC)
Agenda For Murder (ABC)
Rest in Peace, Mrs. Columbo (ABC)
Caution: Murder Can Be Hazardous To Your Health (ABC)
Columbo and The Murder Of A Rock Star (ABC)
Death Hits the Jackpot (ABC)
A Trace of Murder (ABC)
Ashes to Ashes (ABC)
Columbo Likes the Nightlife (ABC)
Red:
Lady in Waiting
Short Fuse
Blueprint For Murder
Dagger of the Mind
Lovely But Lethal
A Case of Immunity
A Matter of Honor
Last Salute to the Commodore
Grand Deceptions (ABC)
Murder, A Self Portrait (ABC)
Uneasy Lies The Crown (ABC)
Murder in Malibu (ABC)
It's All in The Game (ABC)
Butterfly in Shades of Gray (ABC)
Undercover (ABC)
No Time To Die (ABC) ...absolutely the WORST of all Columbo episodes
A Bird In The Hand (ABC)
Strange Bedfellows (ABC)
Murder With Too Many Notes (ABC)
Thanks, Fred...but I think there were a few more of the original series that deserved to be green....but i'm just going to let the list sit as I posted it...
And honestly, other than No Time to Die, I genuinely like all Columbos :)