Change Plotly scatter plot color

Question

I am trying to visualize a 4-class dataset via plotly.

For the following code : fig = px.scatter_3d(df_pca, x='pca1', y='pca2', z='pca3', color = 'emotion')

I get the below graph which is not convenient to understand because the "blue" and "purple" colors are "indiscernible".

So I would like to change the "purple" color to "yellow". Could you please advise how to do it in plotly? The documentation does not seem very helpful.