Secondly, they aren't white.. While some double merle dogs are almost pure white, they can go the complete range all the way up to a dog that you would think is a just a normal merle (most fall somewhere in the middle).
In between five and six months, your baby usually starts to sit up with your help, holding his head in an upright position, keeping the back straight. He may even be able to sit for a second or so without taking any assistance from you, before toppling down after a while [1] .
Your baby will start to learn to sit at about the same time as she's managing to roll over and hold her head up. The muscles she needs to use develop gradually from birth, and she finally becomes strong enough to sit between four months and seven months.