For old yellowish concrete I used a color labeled "sandstone". Since every brand is different, the best thing to do is find a picture of what you want and take it to the store with you. Most craft paints I've seen have either a clear bottle or a paint sample on the lid, s matching isn't too difficult.
Since concrete also ages differently in different regions, and with different aggregate, matching a picture will also ensure that your concrete is suitable for your location and era.