My son is two going on three weeks old when can he go sit outside on the porch in the shade.someone mention colic to me so i don't know what's safe fo?

It's fine: It is perfectly fine for you to take your newborn outside. It's all old wives tales about problems with colic just because you breath outdoor air. The fresh air is excellent for him, as is getting out into the world and experiencing life!. You are right to keep him in the shade, and don't overdress him. Clothes you are comfortable in and one light layer more. Enjoy the outdoors and congratulations.

Careful w exposure: There's no magic age. You need to be careful about exposure: no direct sunlight because he can burn easily; no direct contact with people with colds or unwashed hands; no overheating because of risk of dehydration. Colic isn't really relevant. Not contagious & he'll develop it or he won't (usually by around 6 weeks). Congratulations and good luck. It's an adventure!