In total mess.. Customer wants Swiss Meringue Chocolate Butter Cream frosting. She needs a regular chocolate -dark brown color of it.. I thought I'd make it darker with wilton brown color gel.. I used 1 full bottle of color to 1 batch.. & still NO change at all..Can you please please please let me know how do I make it darker.. I don;t have spray machine ..& Wilton does not carry brown spray

Gel color is a no-no for the meringue buttercreams, as they tend to leave streaks and just give an overall sucky result. What you need is dark brown CANDY color, these are typically oil-based.

you could've added melted chocolate...and when it's not dark enough yet, then you can add the color. Black would even make it darker, but would not take the whole bottle to do it.
 

As far as I know, candy colors don't come in brown.  I second the idea of adding melted dark chocolate, maybe black candy coloring, and you can also make a paste of cocoa powder and hot water to add.  Bottom line though, you may never get it as dark chocolate colored as you like - SMBC just is a light icing.

AYou could also add dark Dutch process cocoa (23-25% cocoa content) that has been dissolved in hot water then cooled.

Red and Green make brown if you want to mix your candy color..