All season long, we constantly battle broadleaf weeds on and around the golf course. This is normal for any golf course or grass yard. Unlike annual grasses like crabgrass or goose grass, there are no pre-emergent chemicals that are applied prior to germination. Broadleaf weeds (like clover or dandelions) are easy to treat with a post emergent herbicide sprayed on the foliage. A selective herbicide will eradicate the weed and not harm the surrounding turf. A popular example of a selective herbicide in the home owner market is, Ortho's Weed-B-Gone.
Yellow Oxalis is a weed that is often confused with white clover. Without looking at the leaves closely, the two are very similar. Both leaves are dark green, of course. There is a small lawn in front of the GM house that occasionally has oxalis growing amongst the turf. However, the leaves are purple. It's the only place on the whole property that I've seen said weed. It's always interesting what you will see in the various microclimates around the property. While purple leaf oxalis isn't anything rare, it only grows in that one spot.