Enabling / Disabling antialiasing for color Picking

It is possible to disable and enable antialiasing when ever you want or only at the creation of the context, as indicated hereafter:

gl = canvas.getContext("experimental-webgl",{antialias:false});

I am trying to develope a picking method base on color tagging. The problem is that I have to pick lines and if they are antialiased the color in the border is different from the color tag.
Any clues or alternative approaches ?