the safe answer: whatever you want that makes YOU comfortable!!

actually, I cut-out something a few years ago from Bicycling Magazine on what to wear when the temperature is XYZ degrees -- it is a really good guideline as to what to wear, but not necessarily exactly what I would wear, but it gets me started in the "general direction". At 70 degrees they suggest base layer: short sleeve jersey and shorts.

so, I would suggest start with base layer and add/subtract based on your internal body temperature -- eveyone is different! good luck.