in mymobile setting I read:

Mobile theme color swatcht:
Toggle the color swatch of the theme between grey and light/blue.

but within the select the only available colors are: light and grey.

To fix it, simply change $string['colourswatch_desc']
from
'Toggle the color swatch of the theme between grey and light/blue.';
to
'Toggle the color swatch of the theme between grey and light.';

in theme/mymobile/lang/en/theme_mymobile.php)

OR

$string['light'] = 'Light';
to
$string['light'] = 'Light/blue';

in the same file.