I agree; it looks kind of strange, especially with shorter ones that end at the waist, because the lower half of the thawb tends to balloon out when the cardigan is buttoned/zipped. If you could find a longer cloak or something like that, it would go better. But with a white thawb, a darker color, like green, brown, black, grey, etc. would look good. I wouldn't pair white with a light color.