I have a 40 metre lead made up of 1.5mm2 cable and it's fine with the immersion heater on and a fan heater on low plus battery charger, I always fully unroll it though otherwise it will be a heater in it's own right, I also have a couple of shorter leads made from old site leads with the plugs changed.
It's not the external size that counts it's the mm2 of the conductors, as long as they can handle 16A it will be fine, the chunky stuff is generally more flexible at colder temperatures (called arctic cable) but no higher rated.
If you have a 32A to 16A converter (usually home made) it should have a fuse inside the plug to protect the cable in case of overload.
My long lead is a screwfix regular extension lead with plug changed, I use a 13A plug to 16A socket converter at the boat end inside the cockpit when I need the length.
Blue is the proper colour for 240V leads but yellow (110V) shows up better in grass to less of a trip hazard, the colour does not change the current rating of the lead at all.