Chromatic Aberration — those purple, green, yellow, and red bands of color at high contrast points in a digital image — is commonly associated with “economy” lenses, but it can show up even with the most expensive optics. Prior versions of Lightroom have had a fairly effective tool to minimize CA — but the new Lightroom 4 kicks it up several notches.
Lightroom 4.1RC2 includes additional control sliders in the Lens Correction panel — although often a simple application of the automated lens profile will be enough to take care of the problem.
If a manual attack on the problem is what is called for, you have several choices of method including using an eyedropper tool to identify the particular hue of the offending band. You can even use the Brush (K) tool to defringe in selected areas — great if one of the fringe colors is usefully prominent in the rest of your image.
I’d suggest “cleaning up” your photo first with all the usual adjustments of tone, contrast, and exposure settings — some of which might reduce the need for CA corrections. Then, as a finishing touch, zoom in to 200% or more and make your image perfect by banishing those rogue strings of color to the recycle bin.