I know it is ironic, but I find the fabric of my black abayas are always lighter and cooler than my coloured ones. No matter what brand, unless you sew your own, they just don't make the coloured fabric abayaat the same quality as black abayaat from the khlaeej. And I don't wanna be hot. So in the summer I usually opt to wear shorts under my abaya (unless I am visiting women, then I wear a long skirt or at-least capri length pants) and a tee or tank, and cover up with a quality fabric black abaya. I have a plain black abaya which is a wardrobe fave, since I get to mix and match it up with 'bout everything I have. An oversize black bag from Suzy Shier ($25.00 CAD) and python-print gladiator sandals (I post heels in my collages but don't encourage you to wear them---they look more visual in a collage but in IRL under the hem of an abaya a heel or a flat the fat looks the same and is close to what the sahaba would have worn). With some cute costumer rings (love fake emeralds) :D and a bottle of water, I am good for hitting the streets to make it out on all my errands and sight-seeing:P
Plain black abaya from http://www.sunnahstyle.com/product_info.php?pName=plain-classic-closed-abaya&osCsid=92a0f4069979130300457283b149d376 (just cut off the tassels). I LOVE THE WEBSITE it is from, btw.