Periwinkle refers to a few different things: a plant, a color, and a small sea snail. The most common association is with the flowering plant, often called vinca, which is a low-growing, trailing evergreen groundcover with star-shaped flowers in shades of blue, purple, pink, or white. The plant is known for its hardiness and ability to thrive in various conditions, including shade and dry soil. Periwinkle also refers to a color, a purplish-blue hue, reminiscent of the plant's flowers. Finally, a periwinkle is also a small marine snail, typically found on rocky shores. 

Here's a more detailed breakdown:

Periwinkle Plant (Vinca): 

Types:

There are two main types of periwinkle: Vinca minor (lesser periwinkle) and Vinca major (greater periwinkle). 

Appearance:

Vinca minor has smaller leaves and flowers than Vinca major. The leaves are typically dark green, glossy, and oval-shaped. Flowers are usually blue-purple, but can also be white or pink depending on the cultivar. 

Growth Habit:

Periwinkle is a groundcover with trailing stems that root easily, allowing it to spread and form dense mats. It can grow in a variety of conditions, including shade and dry soil. 

Uses:

Periwinkle is often used as a groundcover, for erosion control, or as an ornamental plant in window boxes and planters. It is also known for its long flowering period and tolerance to various growing conditions. 

Periwinkle Color:

• A shade of purplish-blue, reminiscent of the periwinkle flower.
• Often used in nail polish and other decorative applications. 

Periwinkle Snail (Littorina littorea):

• A small, edible sea snail found on rocky shores.
• Also known as a "winkle".
• Has a robust shell, often dark and sometimes banded.
• Moves on a muscular foot.