SOLVED. Regency romance, colorful dandy with unconventional protege who rescues kid from pool. Possible Spoilers ahead.

[SB]

I read this book some two years ago.
Regency period I think, set in London. It is about a young girl come to enjoy her season in town. I don't remember quite why, but there is this colorful dandy who takes her under his protection. Because he always dresses in colorful clothes, she believes him to be batting for the other team and thus, thinks herself and him to be safe from any romantic feelings.
However, she comes to love him.
I also remember a scene in which she rescues a kid that has fallen into a lake.

Kind thanks to anyone who can guess the title from this jumble of remembered tidbits!

[SB]

SOLVED SOLVED SOLVED
The famous heroine by Mary Balogh