Feature request: colormap with background

Code Sample

import folium
import pandas as pd
import folium.plugins

import branca
import branca.colormap as cm

data = [
    [33.823400, -118.12194, 99.23],
    [33.823500, -118.12294, 95.23],
    [33.823600, -118.12394, 91.23],
    [33.823700, -118.12494, 90.00]
]

df = pd.DataFrame(data, columns=['latitude','longitude','data'])

x_start = (df['latitude'].max() + df['latitude'].min()) / 2
y_start = (df['longitude'].max() + df['longitude'].min()) / 2
start_coord = (x_start, y_start)


colormap = cm.LinearColormap(colors=['red','lightblue'],
                             index=[df['data'].min(),df['data'].max()],
                             vmin=df['data'].min(),vmax=df['data'].max())

colormap.caption = 'Data [units]'

map = folium.Map(location=start_coord, zoom_start=12)


lat = list(df.latitude)
lon = list(df.longitude)
dat = list(df.data)


for loc, p in zip(zip(lat, lon), dat):
    folium.Circle(
        location=loc,
        radius=10,
        fill=True,
        color=colormap(p),
        fill_opacity=0.7
    ).add_to(map)

map.add_child(colormap)
map.save('index.html')

Problem description

Code above creates colored points, and displays a colormap to show what data value each color corresponds to. This is great but it would be even better if a background colour could be selected. This slightly hacky work-around does exactly what I want:
https://stackoverflow.com/a/50427006/4988601

I'd be happy to try and plumb this into folium itself if a few people show some interest in this feature (I'm fairly new to folium so any pointers on what methods/classes I'd need to poke around in would be appreciated).

Expected Output

Colormap with an optional background color rectangle to help it stand out.

Output of folium.__version__

0.10.0

まず branca.colormap クラスと、例で使用されている生成済みの colormap HTML を調べます。colormap がどのようにレンダリングされるかを追跡し、オプションの背景矩形をどこで表現できるかを特定します。既存の例が、カラーマッピングを変更せずに背景色を選択できるようになれば完了です。