I know I sound like a broken record, repeating this in every post, but you should never use "Trigger once" condition with objects that have multiple instances! And don't use it in loops.
If there is no parent event for the events on your screenshot, then the second line runs on every tick, changing the value of newColor variable 60+ times per second. So the color will be unpredictable when it's time to spawn a new molecule.
Also, using "Pick last created" inside of "For each" loop doesn't make sense. And "Every tick" inside of "Every 5 seconds" is meaningless too.
Basically, the way you organize events is wrong. The whole thing should be done in a single event or function.