Sone do that. It means your battery is partially chargrd. It will go green when it's done.
Also, the speed it changes will slow down as it charges. Dont take it off too soon ( although it wont hurt it) it just might not be fully charged. I usually give it 3 - 4 hours.
These batteries do not have a memory so you can charge it whenever. You dont have to wait for it to fully discharge