Yes Sir... u r some what right... There is a yellow(amber) signal between double yellow and red... Which give us indication to slow our speed in this block because at next signal can be a red...so yellow is for caution
So double yellow does not indicate fully slow down u r speed so slightly slowing the speed can help loco pilot to slow down more later if he see's a yellow next... Or speed up if he see's Green next...
I Hope i m clear and correct :)