Translation:Thank you for your red envelope.
For those not aware, red envelopes are given to children during the New Year, and parents and family put money inside.
It is given by parents to children and by married couples to non-married relatives of the younger generation, usually nieces and nephews. If you aren't married yet you don't give them (traditionally).
Red is auspicious and represents good (fortune, etc.) so it is traditional marriage clothing is red
Yellow represented royalty and at one point commoners were forbidden to wear yellow
White was for mourning and also purity
During celebrations, it's used to watch it off evil spirits. Chinese people say that evil spirits do not like the color red and so they stay away.
I heard somewhere that blue (sort of an opposite to red) is associated with ghosts and death. I guess that's part of it?
The invitation to a wedding can be (jokingly?) called a 紅炸彈 ("red bomb") in Taiwan, because they require the giving of red envelopes, and sometimes arrive when you don't expect.
In Singapore & Malaysia, we call that "red packets", which is its literal translation.