what I understand, your's is a 4-way system. To control a light from 3 switches, you need 2 3-way switches and a 4-way switch. Three 3 way switch will not work. These websites will explain more in detail. http://www.wfu.edu/~matthews/courses/p230/switches.html http://www.danswiringpage.com/
HTH

blink is correct that you need a four-way switch to control a light from three locations. From what you described, your wiring is set up for a four-way switch. Your question is thus about four-way, not three-way swithces.

The box with the two pairs of color-matched wires is for the four-way switch. It gets wired between two three-way switches, and I think the two pairs are the traveller wires that go to those three-way switches (one from each pair going off in each direction, such that unmatched pairs go off in each direction to opposite three-way switches).

The four terminals on a four-way switch are often colored differently in pairs, as well (often two made out of copper and two made out of brass). Sometimes the terminals are also marked in pairs, two for "line one," and two for "line two". Connect one pair of color-matched wires to one pair of color-matched terminals, and the other pair of wires to the other pair of matching terminals. There might/should be another wire running through the box that is just wire-nutted together. That is either your common wire that completes the three-way circuits or a neutral wire that goes to the light.