As the title states, the summer sandals are not dyeable, despite being a level 1 item most likely used for glamour. It would be nice to dye them to match the summer swimwear since some swim wear can be dyed (did not check if all can be dyed); however, it is the only pair of footwear that match the swimwear perfectly.
Not sure if this is an oversight or working as intended, but I would like to make a request to the developers to allow the summer sandals to be dyeable.