So karukan かるかん is not entirely just Okinawan– it is also a famous sweet from Kagoshima prefecture (Kyushu). But it is so common in Okinawa, many people in Okinawa consider it to be an Okinawan sweet. I have not tried karukan from Kyushu, so I am not sure if the taste is the exact same as the Okinawa taste, but I suspect it is very similar.
Karukan comes in pink/red (赤) and white (白), representative colors for celebrations. In the middle is a sweet bean paste, with a somewhat spongy outside. It is steamed sweet bread incorporating Japanese yam. It is actually very delicious, and a little different from a typical manjuu 饅頭.
Karukan is very common and easy to find in Okinawa, just look in any grocery store, sweets shop, or even sometimes in the convenience store! You can probably even find it in omiyage お土産 (souvenir) shops. It is commonly places on altars during Obon, or given as small gifts during celebratory events.