an Old World plant with flat five-petalled, typically bluish flowers and glossy leaves. Some kinds are grown as ornamentals and some contain alkaloids used in medicine.

a purple-blue colour like that of a periwinkle flower.

noun: periwinkle blue; plural noun: periwinkle blues

"the sky was a clear periwinkle and the sun sparkled like a shiny jewel"

And then there are the other, 'Periwinkles'.

Meaty like clams and as sweet as oysters, periwinkles are a delicious seafood option that often goes unappreciated.

Common periwinkle - Wikipedia

Periwinkles

I have shucked (and slurped) my fair share of oysters in my time, but was never enamored with regards to snails. Even if I like this ones name (Periwinkle).

Periwinkle may also be called vinca or myrtle (does that name sound familiar to Harry Potter fans?), and there are 12 species of periwinkles.  The perennial periwinkle and the bedding plant are not the same thing.  As a color, periwinkle will appear as a pale indigo shade and it sits between blue and purple on the color wheel.   

8 hours ago, drpaladin said:

Periwinkle is considered invasive and will choke out all plants in its area.

Sometimes that’s a good thing. If you don’t have something growing on every square millimeter, then a worse weed will grow there.

50 minutes ago, JamesSavik said:

Sometimes that’s a good thing. If you don’t have something growing on every square millimeter, then a worse weed will grow there.

However, it can change ecology and hydrology of the area, meaning how water is able to move across the land.  

I’d much rather have Periwinkle than kudzu any day! Kudzu is the worst of a host of bad stuff that makes Periwinkle look well behaved in comparison.

15 hours ago, drpaladin said:

Periwinkle is considered invasive and will choke out all plants in its area.

I didn't know that. We had it as ground cover all over our yard when I was growing up. 

Maybe that's why it was all over our yard. lol

8 hours ago, JamesSavik said:

I’d much rather have Periwinkle than kudzu any day! Kudzu is the worst of a host of bad stuff that makes Periwinkle look well behaved in comparison.

I agree with you about 'Kudzu'. The worst part is, we have only ourselves to blame for it being here. It was originally government sanctioned and actually paid farmers to plant it. If only we knew then, what we know now. Truth is often stranger than fiction!

Kudzu - Wikipedia