There are three Special Colored hidden Chao eggs found in Adventure Fields.

Shiny Silver Egg - This is found in the Mystic Ruins adventure field by going to the waterfall area. Go into the lake and look to the right. You will see a strange wall panel walk up to it and push it and the chao egg will come out from the waterfall.

Shiny Gold Egg - Go to the area where Sonic fought Chaos for the first time. Look at one of the palm tree area's and you will see an egg shaped rock pick it up. Take it to the antique store and pick up the gold egg and put the stone in its place.

Normal Onyx Egg - Go to the egg carrier prison cell. Where Amy was locked up in one of the cells there is the onyx egg step on the switch to open the cell cage to retrive the egg.

NOTE: These eggs can only be obtained once per game file