Occasionally the difference between one white wine and another is visible, by simply observing the two wines. At one end of the spectrum, white wines can almost completely lack color; at the other end are wines that are amber or deep yellow. White wines may be pale greenish, straw-coloured, golden, or with an orange tinge, thought they are never literally 'white.'
Some white wines may be deeper in color than others because they originated that way.
The type of grape that created the wine, and the growing conditions of the grapes--such as temperature, amount of rain and such--are factors that determine a wine's color.
But sometimes a deep color in a white wine can result from poor storage or age. If a wine automatically looks dark to the eye, give it a taste to decide whether it is still fresh. If the wine has a slightly 'cooked' smell, or if it seems flat when you smell it (dull, lacking primary aromas of the grape from which its made) you're probably looking at a poor or too-old wine.