I've got BLOOD RUSH (ENAMORED) zombie skin, but it doesn't show in wardrobe - special skins section, and I'm afraid if I change skins it'll go away as it happend with my android skin. please help. (i use chrome on xp)

They will appear sometime after the final stage is there (probably once the staff are on/notice that all of the new strains have hit that stage). You're only on stage 7, which isn't the final stage and can't change it (I don't think ?). Usually it's 8 stages, but they might have changed it this year.

Oh! so you can start biting before you reach final stage? I didn't know that

You can start biting at stage six.

Yep ! Stage 6 is when you can start biting for all strains. The only exception to 8 stages so far has been the 2010 strains, which had 6 stages.