There is a bug in the PHP 5.5.9 and PHP 5.5.10 libraries that causes published images to appear unusually bright, as if their exposures were ramped up by 4 stops. If you are experiencing this problem, contact your web hosting provider and request they upgrade their PHP library to 5.5.11 or newer. This will resolve the problem.
If your web host is unwilling or slow to make the change, we recommend going to Settings > Image Publishing inside Koken, unchecking the Use default settings checkbox next to Quality/Sharpness and reducing all sharpness values to zero (0). This can serve as a temporary workaround until your web hosting provider has a chance to properly remedy the issue.