make selected city different color - bubble graph

hello

in the attached graph, i have the map showcasing items sold per city at different times of the period.

i have created a drop down list, and i was wondering if i can get some help making the graph go "red" or different color than the rest of the graph, when i select a city from the drop down list.....im out of ideas and ways, so i would be grateful if someone can help me with this matter.

(i.e. if i select "new orleans" from the drop down, is it possible to make "new orleans" only go red?

thxs, cheers