I don't thing repeating a reference to blue is the rough spot in your formulation. It's the restatement, in different words, an attribute of blue ( tranquility = trust and serenity) that you only just stated two sentences earlier.

Take this example:  
> 1. Jim and John are doctors. They live active lives. Jim likes to golf.  
> 2. Jim and John are doctors. They live active lives. Jim practices medicine and he likes to golf.
> 3. Jim and John are doctors. They live active lives. Jim, mentioned previously, practices medicine and he likes to golf.   
> 4. Jim and John are doctors. They live active lives. Jim not only practices medicine, he also likes to golf.

You should see that case 1 is succinct and quite readable without distraction or loss of meaning. Mentioning Jim twice had no deleterious effect.

It's easy to see that case 2 repeats a fact about Jim twice in a short span. (I don't want to quibble about it being more specific in the second mention.)

Case 3 points to the fact that Jim was mentioned previously. It's awkward, and taking out the remark about our the previous mention gives case 1, which is readable.

Case 4 makes use of the back reference, not to the subject, Jim, but to an attribute about Jim. It is overly wordy, not succinct, making it difficult to read. (If the reader has to pause and ask why a formulation was used, then it's distracting.) Written with the phrase "not only", this back reference can be taken to emphasize Jim's ability to handle two activities at once in his life. But is it really a point worth emphasizing?

Maybe in your example, it is a point worth emphasizing. It appears to be THE point you are emphasizing, as introduced in the next-to-last sentence:

> Why does red infuriate bulls? Or why does blue tranquilize humans? And that's not all. *To us a single color can represent different emotions, sometimes contrasting ones.* Not only does blue relate to trust and serenity; it also relates to coldness, sadness, and lack of emotion.