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] .
All these movements will help baby to develop the muscles that will help them sit on their own. When your baby is around 6 months old they are likely to have developed enough head control to be able to raise their head independently, and may be able to prop themselves up in a sitting position.