To follow on from Megan's points - if the dew point and temperature of the air are the same you would normally expect cloud/fog to form but that will only happen if there are hydroscopic nuclei available (dust, salt, etc) for the water to condense on to.
From Bobakat's story, it is quite common to end up with the windscreen freezing over if you descend from clear, cold air (cold airframe) into warmer, moist air.
Most airliners are not allowed to get airborne with visible frost on the wings (some exceptions on some aircraft if above the wing fuel tanks).
If you don't have visible frost on the blades then you will be OK to fly (remaining VMC) but avoid cloud/fog or visible moisture below 5 degrees C.
Kinetic heating keeps the tips warm enough.