If something is murky, it is hard to see through and unclear. If someone is being murky, their intentions or meaning are unclear - usually on purpose.

You need to supply the whole sentence. Murky means dark, gloomy, dismal, grey, dull, obscure, dim, dreary, cloudy, misty, impenetrable, foggy, overcast, dusky, nebulous, cheerless . Now I have read your explanation to iuui, your expression means "ok, be gloomy " [ unhappy]

I would go with "foggy".