The color of a ripe pineapple can vary by variety so the best rule of thumb is to pick one that has a good fragrant smell and that gives just a little to a very firm grip.
To slice a fresh pineapple remove the top with a long sharp knife and remove enough from the bottom to create a flat surface. Then, stand the decapitated pineapple up and slice the rest of the skin off in long even sections. This will result in an octagonal fruit. Finally, slice the pineapple into quarters and remove the core. Slice as directed.