Thank you for deciding not to buy any more dyed fish!! That is a terrible thing they do to them just for money.
Anyway, I wouldn't be too worried about your fish right away as they need some time to settle in. Often new fish don't eat or hide all the time. Just give them time to get used to their new home.
Also, tetras need to be kept in shoals (groups) of at least six. Don't add any new fish for a while now, but you should eventually add some more Black Widows to help them feel secure. Sorry if you already know this, I just automatically tell it to everyone.

Oh, and I'm assuming the painted tetra is a dyed albino version of the Black Widow, so I think he should shoal fine with the regular ones. And good luck with your new fishies!