You did post a picture, but not a closeup of any yellow leaves. As far as can be seen it looks healthy to me. Al

Sorry here is a close up.

It still looks healthy to me. Leaves will get tattered in the wind and burned in the hot sun. Unless you protect it from the wind and sun by growing it in a greenhouse, you should expect imperfections on the leaves.

If you get water on the leaves when the sun is high and hot, the leaves will burn where the water is. Your photo makes new think this might be the case

You've got a newly planted plant heading into summer. It looks a bit sunburnt is all. Keep it well watered all summer--it's going to need it. You may need to give it some temporary shade such as a trash bin sitting on the south side of it to block some of the sun in the hottest part of the day.

Having said that, you did plant it at the right time, because Bougainvillea should be planted when the soil is warm.