Colors in a scatter plot

[jjj]

Hi

I have the following issue with a scatter plot (here a map with google map).

A map displays  for all my customers  the store they use to shop. I can distinguish the stores with a distinct color on the dots.

I have 2 dimensions :    Id_Customer and Id_Store

Expressions are :  Longitude, Latitude

I have also a list box with Id_Store.

When nothing is selected in the list box, it works fine.

Wher I select 2 or more stores => OK

BUT when I select, just one store,   all the customers are displayed with distinct color. I don't want this, just one color.

I try to creare an expression in the first expression

=if ( Only(Id_Store) > 0  , color(1) , Null() )

It doesn't work.

Any ideas ?

JJJ