Aqui não há contexto para saber se as meias são "dele" ou "dela". Logo, por que não aceitar "Your socks are purple"?or "His socks are purple"?
I am probably going to regret commenting this but did anyone else think of Kingdom Hearts after seeing the Portuguese pronunciation? Oh Roxas.....
It says "your socks are purple" and "his socks are purple" are valid, but not "her socks are purple" ?
before I was marked wrong when I translated as "your socks" so the translation is not consistent with the first time at this level
"suas" is not clear. It could be your plural or singular, her, his, their (speaking to someone about others' socks), etc.
edit There was an indication of Chiefly US informal, but if someone agree with @kcmurphy you/they could click ^ (up) under his/her comment, or say something so as to know more.
But it is not generally accepted, and it is definitely not accepted in (modern) formal writing.