The Slate-colored Junco, Junco hyemalis, is a member of the family Emberizidae which is one of the families split from the family Fringillidae because of genetic studies. This little grey bird will hybridize with other closely related species where their ranges contact which makes identification in some cases difficult. Pictured here is the kind that appears in north central and west Texas.
Nowadays, the Slate-colored Junco is more correctly called the Dark-eyed Junco. As you can see, they are slate or lead gray on the head and upper body with a creamy white or buff belly. Their bills are pinkish white and their tails are edged in white. You can read more about the 15 subspecies of Junco hyemalis here and see photos of the 3 main varieties here.
Juncos can be found in forested areas throughout most of north America. They look for seeds and insects on the ground. Most of the Juncos I have seen have been by themselves or with one or two other birds. However, they are known to travel in large flocks.