Sizzling riddle

In the north of Holland you find a sweet village called Nibbixwold. For ages it is crowded by two clans of clever cobolds living in peace together, the clan with the red hats and the clan with the green hats. Love is their basic theme. However, there is something weird about this community. There are no mirrors, no mirroring surfaces, even the whole concept of mirroring is unknown. No cobold knows the colour of his/her own hat and although every cobold can distinguish the color of his/her neighbour’s hat he/she cannot tell his or her neighbour what colour she/he is wearing. Isn’t that strange? 

Then what happens….  For misty reasons one day a message arrives that ALL the red hatted cobolds should leave the village or else they are to be slaughtered. The red hatted ONLY! Every green hatted cobold that joins them will activate the punishment as well. They are given a limited number of days to obey  the command. The number of days they get to their depart, maximally is the total number of the clan of redhats and starts the day after the message arrived.

The message hits the village as a fragmentation bomb. Every single cobold is totally upset. Clearly their peaceful multicolor coexistance will end here. No one knows nor understands who sent this message and why, but fear has taken over senses and they decide to take it serious and prevent the slaughter.

As they have some days left, they decide to organize a gorgeous farewell party first.

But HOW to decide who should leave the village as you don’t know to what clan you belong???

What hat am I wearing? is the thought most heard in the village.

That’s the question....

Hey CoCo Ton, do you know the answer ? :)