Gold lace sensors were designed to give a vintage 50's style Strat sound (crisp top end, "glassy" bell-like tone. Lower output.) They are great for the neck, middle and bridge positions.

Silver Lace Sensors were designed to give more of a "Fat Strat" sound (i.e. 60's/70's Strats). They have an increased output with more midrange.

Blue Lace Sensors were designed to give more of a 50's humbucker sound (PAF). They have slightly increased output over the silver sensors, and they have a warmer tone. They are better suited for the neck position when you're using a Red sensor in the bridge position.

Red Lace Sensors are the high output version with a thicker/hotter humbucker sound than the Blue sensors. They generally have more bottom end and midrange, and are best suited for the bridge position.