Whilst carp are not generally recognised as sight feeders, there are undoubtedly times when they are visually drawn to a food source and bright pop-ups are a classic example of this. It's not surprising therefore, that fluoro pop-ups have proved very effective, particularly if just using a single bait with no free offerings. The winter and spring months are a classic example of this and a single fluoro pop-up cast to a 'showing' fish has resulted in the downfall of many a carp.
But it would be a mistake to think fluoro pop-ups should be just restricted to single bait presentation. Quite often, a fluoro pop-up fished over a bed of bait can fool the wariest of carp and a little 10mm fluoro pop-up mounted above a standard bottom bait can act as a very good visual sight and lead to a bite or two when other methods fail to produce.