Hi @vanis,
Here is an example, with a custom colorbar font size and color. For more attributes see https://plot.ly/python/reference/#heatmap-colorbar.
import numpy as np
import plotly.graph_objects as go
z = np.random.rand(10,10)
data = [go.Heatmap(
z=z,
colorscale='Greens',
reversescale=True,
colorbar=dict(thickness=20,
ticklen=3, tickcolor='orange',
tickfont=dict(size=14, color='orange')))]
layout = go.Layout(template='none', width=400, height=400, paper_bgcolor='black' )
fig = go.Figure(data=data, layout=layout)