I love my peeps and have put them through every experiment, experience and know all 90 by name and sight, I love this game! (as I have loved them all) BUT....
I have completed every aspect of the game I can see, over 90 pop, over 800 DE points, all totems, chief, got the GP Earthquake finally. Have tried it several places such as the camp (all heathen present)and the Circle. What does one do to convert the last red and orange masks? I saw one post that said it was done through the EarthQuake power. It takes so long to recharge, I hesitate to keep trying blindly. Having gone this far I don't want to quit, but just watching the over population run around and accomplish nothing for the last 5 days is not fun.

Just keep trying. None of my last few heathens converted for at least a day, then three converted at once, followed by the final one at the next attempt with the earthquake power.

I have tried earthquake about 5 times on the filthy camp with heathens,
But nothing seems to change. They just continue to "bumble about". Does one have to convert them by dropping a master devotee on a single heathen? I cannot find any hints anywhere on this portion of the game. Advice would be greatly appreciated!

You can convert the blue-mask heathens by dropping a villager on them, but to convert the red- and yellow-masked guards you'll need to use the earthquake power.

Each time a master heathen (purple masks) is converted they drop one of the necklace pieces. You'll find the pieces on the ground near where each heathen was converted. They look rather like a collectable.