All you really need to taste, appreciate and assess olive oil is your sense of smell and taste.
The look or colour of the oil varies quite substantially depending on the type of olive and the processing of the olive. Olive oil should not be clear or white, which indicates it is refined and not from the first pressing. The spectrum of colours displayed by quality olive oils is between a lush yellow and a subdued green.
Before tasting, put the oil in a shot glass and warm it in your hand so it rises a bit above room temperature. You want to quickly suck the oil over your palette with a lot of air, so it evenly coats your mouth and doesn't settle on your tongue.