Green electricity supplier Keystone Energy Services Inc of Los Angeles says it now has more than 7000 customers for its EarthChoice brand of renewable electricity, up from 6000 in April. Customers can sign up for the green product on-line. The company had announced it was spending $1 million on radio advertising to attract new clients. On the eve of Earth Day, Keystone also announced a new agreement with American Forests, a non-profit group, to plant at least 20,000 trees by 2001. Keystone says it will plant a tree for each EarthChoice electricity customer who has bought its product for at least six months. The company says it expects to start the program next month.