Take the following scenario: You have just enough energy to make it through most of a Clockworks run, but need to buy a one tiny bit more at the end. So you put up an energy buy offer on the market and go on down toward the center of Cradle. Several floors later... "You do not have enough energy to continue!" What happened? Well, your offer got buried, and in the meantime, you've completely forgotten about your need for energy! Now that you're already on the lift, all that's left for you is to buy energy immediately at prices higher than you'd like, or hope that a party member is nice enough to tab you for that floor.
I can't be the only one who has had that happen before, right? It's easier to notice when other players are low on energy than it is to notice that you're low on energy yourself, thanks to the rather conspicuous red bar right next to the party HP numbers that never appears for yourself.
I'd like to propose the following method of alerting players when they don't have enough energy to proceed:
When you get to the lift without enough energy to continue down, instead of displaying the required energy amount in the usual blue numbering, change the display to red instead. It's non-intrusive and takes into consideration the possibility of gaining mist during a floor, but still noticeable enough to remind players of their situation.
Your energy interface already gets a purpleish hue when low