Okay. . . is there ANY logic to synthesis, or is it just a shot in the dark everytime?

I've tried to observe the synthesis colors, and the effects of standard, rapid, and careful synthesis on each. My notes look something to the effect of:

Yellow
Careful synthesis
Not standard sythesis, Standard synthesis
Not rapid synthesis

Red
Not careful synthesis
Standard synthesis, Not standard synthesis
Rapid synthesis, Not rapid synthesis, Sometimes rapid synthesis?

. . . etc., etc.

Despite all of my efforts, there are no obvious consistencies, which leads me to believe there is no logic to the synthesis system, like it's just completely random. Which has me hesitant to use it outside of levequests (as I don't want to lose my items trying to synthesize something.)

I've Googled "Synthesis Guide" but all I get are recipe lists.

Have you guys figured anything out? Or at least have any tips I could use?