My bubble tips go through all sorts of cycles that I cannot attribute to anything I do to the tank. Depending on how inflated or deflated they are, the tentacles appear to change colors. Much more green when deflated and more constricted. Sometime they have bubble tips at the end of the tentacle, other times bubbles further down from the tip, sometimes fat finger looking tentacles especially after ingesting a piece of shrimp, other times skinny long tentacles and occasionally shrunken down to a small messy blob. I used to worry about these changes but have come to realize it's all normal for my nems. Used to be one but split a few months ago.