it's a religious obligation for a believing women!
And so we obey, because
Allah says:
An-Nur - 24:31
And tell the believing women to lower their gaze (from looking at forbidden things), and protect their private parts (from illegal sexual acts, etc.) and not to show off their adornment except only that which is apparent (like palms of hands or one eye or both eyes for necessity to see the way, or outer dress like veil, gloves, head-cover, apron, etc.), and to draw their veils all over Juyubihinna (i.e. their bodies, faces, necks and bosoms, etc.) and not to reveal their adornment except to their husbands, their fathers, their husband's fathers, .........

Truly woman are beautiful ,so they have to cover that beauty , her beauty is only for her husbands eyes!
so the abaya should be plain and don't get the attention of others ,it does not have to be black!!
here and in Saudi it's more culture to wear the black abaya.

By the way I don't sweat any more then normal with abaya!You know what I mean,when it's hot it's hot!