get value in form with name as fieldname[]

In php file, I have 3 checkbox input name as color[]:
<input name=color[] value=1> Red
<input name=color[] value=2> Green
<input name=color[] value=3> Blue

I want to use javascript to check user must check at least one Color. But I can’t check by this syntax (color[].value==””)

Can you show me how? Thanks

Also in #PHP _↴