i want to change the color of my them and i get this error message:

• The specified file sites/all/themes/md_classic/logo.png could not be copied, because the destination directory is not properly configured. This may be caused by a problem with file or directory permissions. More information is available in the system log.
• Warning: imagepng() [function.imagepng]: Invalid filename in _color_render_images() (line 562 of /www/htdocs/w007d194/hak2012/modules/color/color.module).
• The specified file temporary://filekthKjh could not be copied, because the destination directory is not properly configured. This may be caused by a problem with file or directory permissions. More information is available in the system log.

any ideas?