Icons without a color not displayed

Problem/Motivation

Icon styles without a color are not shown.

Steps to reproduce

1. Create an icon style. Specify an existing image path. Do NOT enter a value in the Style options for the RGBA color.
2. Upon saving the style, the image is not shown.

Proposed resolution

This comes from a javascript error when acting on the undefined color. Please find a patch fixing it.

Thanks for considering this.