There are a number of Franciscan Orders which wear gray habits.
Franciscans
Conceptionists, or nuns blonging to the Order of the Immaculate Conception. They are Roman Catholic.
No. There are some Christian groups who do not approve of women wearing and jewelry or "adornment." If these groups considered the cross to be "jewelry," then women of those groups would not wear crosses.
They are supposed to wear habits, but many choose not to.
They don"t all. the habits of the Sisters of Charity are Navy Blue- as are those of the sisters of the IHM- Immaculate Heart of Mary. Dominicans wear White habits which may have black veils. Not all Nuns wear Black habits.
Augustinian monks typically wear black habits with a white tunic and scapular. Sometimes they also wear a white or black cincture around the waist.
I assume that by 'ornaments' you mean jewellery or piercings. Some Christian groups are very strict about jewellery but the vast majority of Christians have no rules about jewellery or piercings and are completely at ease with them.
The north wear blue and the south wear gray
You can wear a gray shirt with brown pants, but you might want a real light gray or try a green shirt with brown pants might be better.
You probably could if it's a dark gray
She wears both but in her regular outfit it is gray.
You can wear fuchsia with chartreuse for all I care as long as I don't have to look at you. Seriously: if you like the look, wear it.