They still wear the cap and shades combo, polo shirt with a bulletproof vest, pants with a gun holster and boots. The third one (named "Chemsec 1") is similar in behaviour to the security division.
This variant was added after the Heists Update, and is seen operating around Humane Labs and Research, particularly during GTA Online in The Humane Labs Raid and during a Resupply mission and an Air Freight Cargo Steal Mission. They are identical to the Blackops 2 variant, except they do not wear hats, have sunglasses of different colors and have night vision gear. The third uniform (named "Blackops 3") appears to be a black operations unit.The second uniform (named "Blackops 2") wear heavier equipment than the previous operator, consisting of either a military cap or a ski hat (both with varying color and camouflage patterns), sunglasses, a military jacket or a polo shirt, always with bulletproof vest, tactical pants (with holsters, baggies and knee pads) and boots.Their arms have tattoo designs and may wear a headset when in an aircraft.
Merryweather appears to have several divisions, which is determined by the uniform and equipment they carry: According to their website, Merryweather is shown to be operating around the world, including the US. Merryweather Security is a mercenary group led by Don Percival and dedicated to various military operations. “ Merryweather Security Consulting? Private army of the New World Order? The folks waging outsourced shadow wars in twenty countries around the globe, and recently cleared to operate on US soil? ” - Trevor Philips asking Floyd Hebert about Merryweather.