Not telling the truth for unselfish reasons, for the sole purposes of helping, inspiring, giving others hope, preventing harm to others, is called a white lie.
Telling a child their drawing, something they built, a project they have started, is much better than it actually is, to encourage the child to continue, promotes the child's interest. Telling an older person in rehabilitation they are improving more dramatically then they are in reality, inspires them to not let up, to keep trying, keep working.
People will often tell new parents their baby is the most beautiful child they have seen. When really, the child is not very attractive. But telling the truth does not serve any positive purpose. Whereas telling a white lie, hurts nothing, but makes the parents feel better.
A woman comes to your home, telling you her husband is angry, and out to hurt her. You allow her to hide in your home until he calms down. In the mean time, he comes to your door, still enraged, and asks if you have seen her. Telling him the truth, puts her in danger. While telling a lie, could in fact, save her life, or save her from injury.
So whether a lie is a white lie or not, is based on justification. If it serves to to help, keep safe, inspire others for unselfish purposes, you are justified in telling the lie. If it is for selfish, self serving motives, or to serve in an undeserved, destructive way for others, it is not justified.