"I stood tip-toe upon a little hill"
In this poem, dating from around 1817, Keats writes:
"Here are sweet peas, on tip-toe for a flight:
With wings of gentle flush o'er delicate white,
And taper fingers catching at all things,
To bind them all about with tiny rings"
I like to think that he was referring to the Painted Lady - the earliest variety of sweet pea (or sweet scented pea as they were then called) which was first named in 1752. At that time there were very few varieties. John Abercrombie's "The Universal Gardener and Botanist" published in 1797 lists four so it seems likely that Keats was referring to Painted Lady, it certainly fits his description. By using the words 'wings' and 'flight' Keats may be alluding to the Painted Lady butterfly.