The base color of a leaf is considered to be the color that covers 60% or more of the leaf surface. In hostas, the base colors are Blue-Green, Green and Yellow. Technically, white could also be considered a base color since a few variegated hostas have 60% white leaves.

"Blue" hostas actually have green leaves that are covered with a type of wax or "bloom" which reflects bluish light. Often during the heat of summer this wax melts off and the leaf becomes green in color. Green hostas, of course, have plenty of the green pigment, chlorophyll. The color may range from light green to dark green which may be described as "black". Most fall into the category of medium green. Yellow hostas have a very low level of chlorophyll and the yellow pigment dominates. However, they must still have chlorophyll at some level or they could not complete photosynthesis. The term "gold" is often used but this is actually just a shade of yellow. That is also the problem with predominately white foliage hostas which have difficulty growing and are easily sun scorched due to the lack of chlorophyll.