Many, many flavors, especially fruit flavors, benefit from the presence of a subtle green note. Often it can simply add a subtle hint of freshness to, for example, a ripe banana flavor. Sometimes it can be a very important aspect of the overall character, as in the case of a green apple flavor.
By far the most widely used green character is cis-3-hexenol (CAS# 928- 96-1, FEMA# 2563) and the results of simply adding this ingredient alone can be quite impressive. The resultant green character is attractive and somewhat reminiscent of fresh cut grass. This can be all that is required when the overall green note is only subtle, but it can seem a little too harsh in some flavor types, especially at higher use levels.
Using cis-3-hexenol in combination with a second green note can provide a softer and more attractive option than using the alcohol alone. The most obvious (and by far the most common) choice for a second green note to add complexity is cis-3-hexenyl acetate (CAS# 3681-71-8, FEMA# 3171). This chemical is also predominantly green, but the profile is softer, less like fresh cut grass and more fruity.