CODE EXAMPLE FOR PYTHON

plotly grid lines color

import plotly.express as px
df = px.data.iris()

fig = px.scatter(df, x="sepal_width", y="sepal_length", facet_col="species")
fig.update_xaxes(showgrid=True, gridwidth=1, gridcolor='LightPink')
fig.update_yaxes(showgrid=True, gridwidth=1, gridcolor='LightPink')

fig.show()