Yellow light

From Grandma:

When I told London that she would be sleeping overnight at our house she was
so excited.  But then she seemed a little concerned. 
She said, "Grandma, will you come and wake me up?"  You don't have a yellow
light at your house.

London is talking about the light that lets them know when they can get out of bed. It is green when they need to be in bed and yellow when they can wake up.