Red tops, blue tops, and yellow tops come in many sizes to fit different vehicles. The colors have to do with the different battery types. The blue top is a deep cycle marine battery. Red is for cranking amps. Yellow is for inbetween uses like starting your truck and also running a winch...
Double check the manufactured date code. If it's more than 6 months old, don't buy it. Batteries go bad if they are not charged regularly. Technically, they can charge it and use a sticker to change the date code and any warranties begin timing on date of sale. I don't like that because you have no way of knowing how or when they recharged it. Take your old battery in for an exchange or they will charge you a core charge. Recyclers pay $.15/lb in some places if you don't exchange your old battery.