[TR] 1972 Triumph TR6 spark plug question

[thenicholls at verizon.net]

On my 72 TR6, last year I finally got the carb jets right and the car was running better than ever.
 
I have always used the standard NGK plugs on my car.
 
I have never had any issues with running hot here in Virginia.
 
My concern is after the jets were corrected and the car tuned, the temperture gauge barely comes out into the white part of the gauge.
 
Is it possible for an engine to run too cold?  I had never thought this was a concern.
 
On the topic of plugs, if it is an issue, should I get the colder set or the hotter set, I was never clear after reading the archives on which way to go.
 
Finally, the plugs read very nornal when you compare them to pictures on the web.
 
Any input is appreciated.
 
Craig 
1972 Triumph TR6
Vienna, VA