Yep, it's normal. It's yellow when it considers there's not enough in the battery to run the ECO system.
One example, I'd parked to take a phone call, and the engine cut, as it should, but the aircon continued to run, fans etc.
The phone call was longer than expected, and suddenly, the system must have thought I'd taken enough out of the battery, so it switched the ECO icon to yellow, and started the engine!
(this is why, in the manual, it says not to leave the vehicle unattended when ECO has stopped the engine, as it can restart unexpectedly)
HTH
Malcolm