I agree with those who say
airframe icing conditions are generalised as below 0 degrees Celsius and in less than 1Km viz (i.e. fog).
I have heard that the term 'visible moisture' by definition is moisture causing a visibility of less than 1Km, although i would be hesitant to fly in mist (1-4km) at less than 0 degrees, which incidentally i would say is quite visible
with regards to
engine/carb icing, the temp drop across the carb can (i've heard) be as much as 30 degrees so in humid conditions one must be very careful not to get caught out flying in +30C....
also there is obviously the possibility of freezing rain
under the passage of a warm front, if you're in the cold sector, and rain from the warmer sector above cools to below zero (supercooled) and sticks upon impact, or your airframe is very cold and fly's into the rain... leading to particularly dangerous clear ice.
Aucky