Yes, the secret is temperature. If your room (or yard) is a little too chilly, the turquoise will be most affected, because it's the slowest to react of all of the Procion MX type dyes. I've heard of this many, many times. Here's a page that includes a discussion of different ways to gt the extra warmth you need:
What is the effect of temperature on fiber reactive dyes?The minimum temperature is 70°F (21°C) if you leave your dyed shirts to react overnight (they must be kept moist for the full reaction time, either by using urea in the dye mixture, or by wrapping in plastic). Higher temperatures require less time. Temperatures lower than 70°F almost never work out well. I prefer higher temperatures, just to be sure to take full advantage of the dye I use.
More on this dye:
A Beautiful Blue: Procion Turquoise MX-G.
Paula